use crate::array; use crate::cmp::{self, Ordering}; use crate::ops::{ChangeOutputType, ControlFlow, FromResidual, Residual, Try}; use super::super::try_process; use super::super::ByRefSized; use super::super::TrustedRandomAccessNoCoerce; use super::super::{ArrayChunks, Chain, Cloned, Copied, Cycle, Enumerate, Filter, FilterMap, Fuse}; use super::super::{FlatMap, Flatten}; use super::super::{FromIterator, Intersperse, IntersperseWith, Product, Sum, Zip}; use super::super::{ Inspect, Map, MapWhile, Peekable, Rev, Scan, Skip, SkipWhile, StepBy, Take, TakeWhile, }; fn _assert_is_object_safe(_: &dyn Iterator) {} /// An interface for dealing with iterators. /// /// This is the main iterator trait. For more about the concept of iterators /// generally, please see the [module-level documentation]. In particular, you /// may want to know how to [implement `Iterator`][impl]. /// /// [module-level documentation]: crate::iter /// [impl]: crate::iter#implementing-iterator #[stable(feature = "rust1", since = "1.0.0")] #[rustc_on_unimplemented( on( _Self = "std::ops::RangeTo", label = "if you meant to iterate until a value, add a starting value", note = "`..end` is a `RangeTo`, which cannot be iterated on; you might have meant to have a \ bounded `Range`: `0..end`" ), on( _Self = "std::ops::RangeToInclusive", label = "if you meant to iterate until a value (including it), add a starting value", note = "`..=end` is a `RangeToInclusive`, which cannot be iterated on; you might have meant \ to have a bounded `RangeInclusive`: `0..=end`" ), on( _Self = "[]", label = "`{Self}` is not an iterator; try calling `.into_iter()` or `.iter()`" ), on(_Self = "&[]", label = "`{Self}` is not an iterator; try calling `.iter()`"), on( _Self = "std::vec::Vec", label = "`{Self}` is not an iterator; try calling `.into_iter()` or `.iter()`" ), on( _Self = "&str", label = "`{Self}` is not an iterator; try calling `.chars()` or `.bytes()`" ), on( _Self = "std::string::String", label = "`{Self}` is not an iterator; try calling `.chars()` or `.bytes()`" ), on( _Self = "{integral}", note = "if you want to iterate between `start` until a value `end`, use the exclusive range \ syntax `start..end` or the inclusive range syntax `start..=end`" ), label = "`{Self}` is not an iterator", message = "`{Self}` is not an iterator" )] #[doc(notable_trait)] #[rustc_diagnostic_item = "Iterator"] #[must_use = "iterators are lazy and do nothing unless consumed"] pub trait Iterator { /// The type of the elements being iterated over. #[stable(feature = "rust1", since = "1.0.0")] type Item; /// Advances the iterator and returns the next value. /// /// Returns [`None`] when iteration is finished. Individual iterator /// implementations may choose to resume iteration, and so calling `next()` /// again may or may not eventually start returning [`Some(Item)`] again at some /// point. /// /// [`Some(Item)`]: Some /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// /// let mut iter = a.iter(); /// /// // A call to next() returns the next value... /// assert_eq!(Some(&1), iter.next()); /// assert_eq!(Some(&2), iter.next()); /// assert_eq!(Some(&3), iter.next()); /// /// // ... and then None once it's over. /// assert_eq!(None, iter.next()); /// /// // More calls may or may not return `None`. Here, they always will. /// assert_eq!(None, iter.next()); /// assert_eq!(None, iter.next()); /// ``` #[lang = "next"] #[stable(feature = "rust1", since = "1.0.0")] fn next(&mut self) -> Option; /// Advances the iterator and returns an array containing the next `N` values. /// /// If there are not enough elements to fill the array then `Err` is returned /// containing an iterator over the remaining elements. /// /// # Examples /// /// Basic usage: /// /// ``` /// #![feature(iter_next_chunk)] /// /// let mut iter = "lorem".chars(); /// /// assert_eq!(iter.next_chunk().unwrap(), ['l', 'o']); // N is inferred as 2 /// assert_eq!(iter.next_chunk().unwrap(), ['r', 'e', 'm']); // N is inferred as 3 /// assert_eq!(iter.next_chunk::<4>().unwrap_err().as_slice(), &[]); // N is explicitly 4 /// ``` /// /// Split a string and get the first three items. /// /// ``` /// #![feature(iter_next_chunk)] /// /// let quote = "not all those who wander are lost"; /// let [first, second, third] = quote.split_whitespace().next_chunk().unwrap(); /// assert_eq!(first, "not"); /// assert_eq!(second, "all"); /// assert_eq!(third, "those"); /// ``` #[inline] #[unstable(feature = "iter_next_chunk", reason = "recently added", issue = "98326")] fn next_chunk( &mut self, ) -> Result<[Self::Item; N], array::IntoIter> where Self: Sized, { array::iter_next_chunk(self) } /// Returns the bounds on the remaining length of the iterator. /// /// Specifically, `size_hint()` returns a tuple where the first element /// is the lower bound, and the second element is the upper bound. /// /// The second half of the tuple that is returned is an [Option]<[usize]>. /// A [`None`] here means that either there is no known upper bound, or the /// upper bound is larger than [`usize`]. /// /// # Implementation notes /// /// It is not enforced that an iterator implementation yields the declared /// number of elements. A buggy iterator may yield less than the lower bound /// or more than the upper bound of elements. /// /// `size_hint()` is primarily intended to be used for optimizations such as /// reserving space for the elements of the iterator, but must not be /// trusted to e.g., omit bounds checks in unsafe code. An incorrect /// implementation of `size_hint()` should not lead to memory safety /// violations. /// /// That said, the implementation should provide a correct estimation, /// because otherwise it would be a violation of the trait's protocol. /// /// The default implementation returns (0, [None]) which is correct for any /// iterator. /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// let mut iter = a.iter(); /// /// assert_eq!((3, Some(3)), iter.size_hint()); /// let _ = iter.next(); /// assert_eq!((2, Some(2)), iter.size_hint()); /// ``` /// /// A more complex example: /// /// ``` /// // The even numbers in the range of zero to nine. /// let iter = (0..10).filter(|x| x % 2 == 0); /// /// // We might iterate from zero to ten times. Knowing that it's five /// // exactly wouldn't be possible without executing filter(). /// assert_eq!((0, Some(10)), iter.size_hint()); /// /// // Let's add five more numbers with chain() /// let iter = (0..10).filter(|x| x % 2 == 0).chain(15..20); /// /// // now both bounds are increased by five /// assert_eq!((5, Some(15)), iter.size_hint()); /// ``` /// /// Returning `None` for an upper bound: /// /// ``` /// // an infinite iterator has no upper bound /// // and the maximum possible lower bound /// let iter = 0..; /// /// assert_eq!((usize::MAX, None), iter.size_hint()); /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn size_hint(&self) -> (usize, Option) { (0, None) } /// Consumes the iterator, counting the number of iterations and returning it. /// /// This method will call [`next`] repeatedly until [`None`] is encountered, /// returning the number of times it saw [`Some`]. Note that [`next`] has to be /// called at least once even if the iterator does not have any elements. /// /// [`next`]: Iterator::next /// /// # Overflow Behavior /// /// The method does no guarding against overflows, so counting elements of /// an iterator with more than [`usize::MAX`] elements either produces the /// wrong result or panics. If debug assertions are enabled, a panic is /// guaranteed. /// /// # Panics /// /// This function might panic if the iterator has more than [`usize::MAX`] /// elements. /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// assert_eq!(a.iter().count(), 3); /// /// let a = [1, 2, 3, 4, 5]; /// assert_eq!(a.iter().count(), 5); /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn count(self) -> usize where Self: Sized, { self.fold( 0, #[rustc_inherit_overflow_checks] |count, _| count + 1, ) } /// Consumes the iterator, returning the last element. /// /// This method will evaluate the iterator until it returns [`None`]. While /// doing so, it keeps track of the current element. After [`None`] is /// returned, `last()` will then return the last element it saw. /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// assert_eq!(a.iter().last(), Some(&3)); /// /// let a = [1, 2, 3, 4, 5]; /// assert_eq!(a.iter().last(), Some(&5)); /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn last(self) -> Option where Self: Sized, { #[inline] fn some(_: Option, x: T) -> Option { Some(x) } self.fold(None, some) } /// Advances the iterator by `n` elements. /// /// This method will eagerly skip `n` elements by calling [`next`] up to `n` /// times until [`None`] is encountered. /// /// `advance_by(n)` will return [`Ok(())`][Ok] if the iterator successfully advances by /// `n` elements, or [`Err(k)`][Err] if [`None`] is encountered, where `k` is the number /// of elements the iterator is advanced by before running out of elements (i.e. the /// length of the iterator). Note that `k` is always less than `n`. /// /// Calling `advance_by(0)` can do meaningful work, for example [`Flatten`] /// can advance its outer iterator until it finds an inner iterator that is not empty, which /// then often allows it to return a more accurate `size_hint()` than in its initial state. /// /// [`Flatten`]: crate::iter::Flatten /// [`next`]: Iterator::next /// /// # Examples /// /// Basic usage: /// /// ``` /// #![feature(iter_advance_by)] /// /// let a = [1, 2, 3, 4]; /// let mut iter = a.iter(); /// /// assert_eq!(iter.advance_by(2), Ok(())); /// assert_eq!(iter.next(), Some(&3)); /// assert_eq!(iter.advance_by(0), Ok(())); /// assert_eq!(iter.advance_by(100), Err(1)); // only `&4` was skipped /// ``` #[inline] #[unstable(feature = "iter_advance_by", reason = "recently added", issue = "77404")] fn advance_by(&mut self, n: usize) -> Result<(), usize> { for i in 0..n { self.next().ok_or(i)?; } Ok(()) } /// Returns the `n`th element of the iterator. /// /// Like most indexing operations, the count starts from zero, so `nth(0)` /// returns the first value, `nth(1)` the second, and so on. /// /// Note that all preceding elements, as well as the returned element, will be /// consumed from the iterator. That means that the preceding elements will be /// discarded, and also that calling `nth(0)` multiple times on the same iterator /// will return different elements. /// /// `nth()` will return [`None`] if `n` is greater than or equal to the length of the /// iterator. /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// assert_eq!(a.iter().nth(1), Some(&2)); /// ``` /// /// Calling `nth()` multiple times doesn't rewind the iterator: /// /// ``` /// let a = [1, 2, 3]; /// /// let mut iter = a.iter(); /// /// assert_eq!(iter.nth(1), Some(&2)); /// assert_eq!(iter.nth(1), None); /// ``` /// /// Returning `None` if there are less than `n + 1` elements: /// /// ``` /// let a = [1, 2, 3]; /// assert_eq!(a.iter().nth(10), None); /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn nth(&mut self, n: usize) -> Option { self.advance_by(n).ok()?; self.next() } /// Creates an iterator starting at the same point, but stepping by /// the given amount at each iteration. /// /// Note 1: The first element of the iterator will always be returned, /// regardless of the step given. /// /// Note 2: The time at which ignored elements are pulled is not fixed. /// `StepBy` behaves like the sequence `self.next()`, `self.nth(step-1)`, /// `self.nth(step-1)`, …, but is also free to behave like the sequence /// `advance_n_and_return_first(&mut self, step)`, /// `advance_n_and_return_first(&mut self, step)`, … /// Which way is used may change for some iterators for performance reasons. /// The second way will advance the iterator earlier and may consume more items. /// /// `advance_n_and_return_first` is the equivalent of: /// ``` /// fn advance_n_and_return_first(iter: &mut I, n: usize) -> Option /// where /// I: Iterator, /// { /// let next = iter.next(); /// if n > 1 { /// iter.nth(n - 2); /// } /// next /// } /// ``` /// /// # Panics /// /// The method will panic if the given step is `0`. /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [0, 1, 2, 3, 4, 5]; /// let mut iter = a.iter().step_by(2); /// /// assert_eq!(iter.next(), Some(&0)); /// assert_eq!(iter.next(), Some(&2)); /// assert_eq!(iter.next(), Some(&4)); /// assert_eq!(iter.next(), None); /// ``` #[inline] #[stable(feature = "iterator_step_by", since = "1.28.0")] fn step_by(self, step: usize) -> StepBy where Self: Sized, { StepBy::new(self, step) } /// Takes two iterators and creates a new iterator over both in sequence. /// /// `chain()` will return a new iterator which will first iterate over /// values from the first iterator and then over values from the second /// iterator. /// /// In other words, it links two iterators together, in a chain. 🔗 /// /// [`once`] is commonly used to adapt a single value into a chain of /// other kinds of iteration. /// /// # Examples /// /// Basic usage: /// /// ``` /// let a1 = [1, 2, 3]; /// let a2 = [4, 5, 6]; /// /// let mut iter = a1.iter().chain(a2.iter()); /// /// assert_eq!(iter.next(), Some(&1)); /// assert_eq!(iter.next(), Some(&2)); /// assert_eq!(iter.next(), Some(&3)); /// assert_eq!(iter.next(), Some(&4)); /// assert_eq!(iter.next(), Some(&5)); /// assert_eq!(iter.next(), Some(&6)); /// assert_eq!(iter.next(), None); /// ``` /// /// Since the argument to `chain()` uses [`IntoIterator`], we can pass /// anything that can be converted into an [`Iterator`], not just an /// [`Iterator`] itself. For example, slices (`&[T]`) implement /// [`IntoIterator`], and so can be passed to `chain()` directly: /// /// ``` /// let s1 = &[1, 2, 3]; /// let s2 = &[4, 5, 6]; /// /// let mut iter = s1.iter().chain(s2); /// /// assert_eq!(iter.next(), Some(&1)); /// assert_eq!(iter.next(), Some(&2)); /// assert_eq!(iter.next(), Some(&3)); /// assert_eq!(iter.next(), Some(&4)); /// assert_eq!(iter.next(), Some(&5)); /// assert_eq!(iter.next(), Some(&6)); /// assert_eq!(iter.next(), None); /// ``` /// /// If you work with Windows API, you may wish to convert [`OsStr`] to `Vec`: /// /// ``` /// #[cfg(windows)] /// fn os_str_to_utf16(s: &std::ffi::OsStr) -> Vec { /// use std::os::windows::ffi::OsStrExt; /// s.encode_wide().chain(std::iter::once(0)).collect() /// } /// ``` /// /// [`once`]: crate::iter::once /// [`OsStr`]: ../../std/ffi/struct.OsStr.html #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn chain(self, other: U) -> Chain where Self: Sized, U: IntoIterator, { Chain::new(self, other.into_iter()) } /// 'Zips up' two iterators into a single iterator of pairs. /// /// `zip()` returns a new iterator that will iterate over two other /// iterators, returning a tuple where the first element comes from the /// first iterator, and the second element comes from the second iterator. /// /// In other words, it zips two iterators together, into a single one. /// /// If either iterator returns [`None`], [`next`] from the zipped iterator /// will return [`None`]. /// If the zipped iterator has no more elements to return then each further attempt to advance /// it will first try to advance the first iterator at most one time and if it still yielded an item /// try to advance the second iterator at most one time. /// /// To 'undo' the result of zipping up two iterators, see [`unzip`]. /// /// [`unzip`]: Iterator::unzip /// /// # Examples /// /// Basic usage: /// /// ``` /// let a1 = [1, 2, 3]; /// let a2 = [4, 5, 6]; /// /// let mut iter = a1.iter().zip(a2.iter()); /// /// assert_eq!(iter.next(), Some((&1, &4))); /// assert_eq!(iter.next(), Some((&2, &5))); /// assert_eq!(iter.next(), Some((&3, &6))); /// assert_eq!(iter.next(), None); /// ``` /// /// Since the argument to `zip()` uses [`IntoIterator`], we can pass /// anything that can be converted into an [`Iterator`], not just an /// [`Iterator`] itself. For example, slices (`&[T]`) implement /// [`IntoIterator`], and so can be passed to `zip()` directly: /// /// ``` /// let s1 = &[1, 2, 3]; /// let s2 = &[4, 5, 6]; /// /// let mut iter = s1.iter().zip(s2); /// /// assert_eq!(iter.next(), Some((&1, &4))); /// assert_eq!(iter.next(), Some((&2, &5))); /// assert_eq!(iter.next(), Some((&3, &6))); /// assert_eq!(iter.next(), None); /// ``` /// /// `zip()` is often used to zip an infinite iterator to a finite one. /// This works because the finite iterator will eventually return [`None`], /// ending the zipper. Zipping with `(0..)` can look a lot like [`enumerate`]: /// /// ``` /// let enumerate: Vec<_> = "foo".chars().enumerate().collect(); /// /// let zipper: Vec<_> = (0..).zip("foo".chars()).collect(); /// /// assert_eq!((0, 'f'), enumerate[0]); /// assert_eq!((0, 'f'), zipper[0]); /// /// assert_eq!((1, 'o'), enumerate[1]); /// assert_eq!((1, 'o'), zipper[1]); /// /// assert_eq!((2, 'o'), enumerate[2]); /// assert_eq!((2, 'o'), zipper[2]); /// ``` /// /// If both iterators have roughly equivalent syntax, it may be more readable to use [`zip`]: /// /// ``` /// use std::iter::zip; /// /// let a = [1, 2, 3]; /// let b = [2, 3, 4]; /// /// let mut zipped = zip( /// a.into_iter().map(|x| x * 2).skip(1), /// b.into_iter().map(|x| x * 2).skip(1), /// ); /// /// assert_eq!(zipped.next(), Some((4, 6))); /// assert_eq!(zipped.next(), Some((6, 8))); /// assert_eq!(zipped.next(), None); /// ``` /// /// compared to: /// /// ``` /// # let a = [1, 2, 3]; /// # let b = [2, 3, 4]; /// # /// let mut zipped = a /// .into_iter() /// .map(|x| x * 2) /// .skip(1) /// .zip(b.into_iter().map(|x| x * 2).skip(1)); /// # /// # assert_eq!(zipped.next(), Some((4, 6))); /// # assert_eq!(zipped.next(), Some((6, 8))); /// # assert_eq!(zipped.next(), None); /// ``` /// /// [`enumerate`]: Iterator::enumerate /// [`next`]: Iterator::next /// [`zip`]: crate::iter::zip #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn zip(self, other: U) -> Zip where Self: Sized, U: IntoIterator, { Zip::new(self, other.into_iter()) } /// Creates a new iterator which places a copy of `separator` between adjacent /// items of the original iterator. /// /// In case `separator` does not implement [`Clone`] or needs to be /// computed every time, use [`intersperse_with`]. /// /// # Examples /// /// Basic usage: /// /// ``` /// #![feature(iter_intersperse)] /// /// let mut a = [0, 1, 2].iter().intersperse(&100); /// assert_eq!(a.next(), Some(&0)); // The first element from `a`. /// assert_eq!(a.next(), Some(&100)); // The separator. /// assert_eq!(a.next(), Some(&1)); // The next element from `a`. /// assert_eq!(a.next(), Some(&100)); // The separator. /// assert_eq!(a.next(), Some(&2)); // The last element from `a`. /// assert_eq!(a.next(), None); // The iterator is finished. /// ``` /// /// `intersperse` can be very useful to join an iterator's items using a common element: /// ``` /// #![feature(iter_intersperse)] /// /// let hello = ["Hello", "World", "!"].iter().copied().intersperse(" ").collect::(); /// assert_eq!(hello, "Hello World !"); /// ``` /// /// [`Clone`]: crate::clone::Clone /// [`intersperse_with`]: Iterator::intersperse_with #[inline] #[unstable(feature = "iter_intersperse", reason = "recently added", issue = "79524")] fn intersperse(self, separator: Self::Item) -> Intersperse where Self: Sized, Self::Item: Clone, { Intersperse::new(self, separator) } /// Creates a new iterator which places an item generated by `separator` /// between adjacent items of the original iterator. /// /// The closure will be called exactly once each time an item is placed /// between two adjacent items from the underlying iterator; specifically, /// the closure is not called if the underlying iterator yields less than /// two items and after the last item is yielded. /// /// If the iterator's item implements [`Clone`], it may be easier to use /// [`intersperse`]. /// /// # Examples /// /// Basic usage: /// /// ``` /// #![feature(iter_intersperse)] /// /// #[derive(PartialEq, Debug)] /// struct NotClone(usize); /// /// let v = [NotClone(0), NotClone(1), NotClone(2)]; /// let mut it = v.into_iter().intersperse_with(|| NotClone(99)); /// /// assert_eq!(it.next(), Some(NotClone(0))); // The first element from `v`. /// assert_eq!(it.next(), Some(NotClone(99))); // The separator. /// assert_eq!(it.next(), Some(NotClone(1))); // The next element from `v`. /// assert_eq!(it.next(), Some(NotClone(99))); // The separator. /// assert_eq!(it.next(), Some(NotClone(2))); // The last element from from `v`. /// assert_eq!(it.next(), None); // The iterator is finished. /// ``` /// /// `intersperse_with` can be used in situations where the separator needs /// to be computed: /// ``` /// #![feature(iter_intersperse)] /// /// let src = ["Hello", "to", "all", "people", "!!"].iter().copied(); /// /// // The closure mutably borrows its context to generate an item. /// let mut happy_emojis = [" ❤️ ", " 😀 "].iter().copied(); /// let separator = || happy_emojis.next().unwrap_or(" 🦀 "); /// /// let result = src.intersperse_with(separator).collect::(); /// assert_eq!(result, "Hello ❤️ to 😀 all 🦀 people 🦀 !!"); /// ``` /// [`Clone`]: crate::clone::Clone /// [`intersperse`]: Iterator::intersperse #[inline] #[unstable(feature = "iter_intersperse", reason = "recently added", issue = "79524")] fn intersperse_with(self, separator: G) -> IntersperseWith where Self: Sized, G: FnMut() -> Self::Item, { IntersperseWith::new(self, separator) } /// Takes a closure and creates an iterator which calls that closure on each /// element. /// /// `map()` transforms one iterator into another, by means of its argument: /// something that implements [`FnMut`]. It produces a new iterator which /// calls this closure on each element of the original iterator. /// /// If you are good at thinking in types, you can think of `map()` like this: /// If you have an iterator that gives you elements of some type `A`, and /// you want an iterator of some other type `B`, you can use `map()`, /// passing a closure that takes an `A` and returns a `B`. /// /// `map()` is conceptually similar to a [`for`] loop. However, as `map()` is /// lazy, it is best used when you're already working with other iterators. /// If you're doing some sort of looping for a side effect, it's considered /// more idiomatic to use [`for`] than `map()`. /// /// [`for`]: ../../book/ch03-05-control-flow.html#looping-through-a-collection-with-for /// [`FnMut`]: crate::ops::FnMut /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// /// let mut iter = a.iter().map(|x| 2 * x); /// /// assert_eq!(iter.next(), Some(2)); /// assert_eq!(iter.next(), Some(4)); /// assert_eq!(iter.next(), Some(6)); /// assert_eq!(iter.next(), None); /// ``` /// /// If you're doing some sort of side effect, prefer [`for`] to `map()`: /// /// ``` /// # #![allow(unused_must_use)] /// // don't do this: /// (0..5).map(|x| println!("{x}")); /// /// // it won't even execute, as it is lazy. Rust will warn you about this. /// /// // Instead, use for: /// for x in 0..5 { /// println!("{x}"); /// } /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn map(self, f: F) -> Map where Self: Sized, F: FnMut(Self::Item) -> B, { Map::new(self, f) } /// Calls a closure on each element of an iterator. /// /// This is equivalent to using a [`for`] loop on the iterator, although /// `break` and `continue` are not possible from a closure. It's generally /// more idiomatic to use a `for` loop, but `for_each` may be more legible /// when processing items at the end of longer iterator chains. In some /// cases `for_each` may also be faster than a loop, because it will use /// internal iteration on adapters like `Chain`. /// /// [`for`]: ../../book/ch03-05-control-flow.html#looping-through-a-collection-with-for /// /// # Examples /// /// Basic usage: /// /// ``` /// use std::sync::mpsc::channel; /// /// let (tx, rx) = channel(); /// (0..5).map(|x| x * 2 + 1) /// .for_each(move |x| tx.send(x).unwrap()); /// /// let v: Vec<_> = rx.iter().collect(); /// assert_eq!(v, vec![1, 3, 5, 7, 9]); /// ``` /// /// For such a small example, a `for` loop may be cleaner, but `for_each` /// might be preferable to keep a functional style with longer iterators: /// /// ``` /// (0..5).flat_map(|x| x * 100 .. x * 110) /// .enumerate() /// .filter(|&(i, x)| (i + x) % 3 == 0) /// .for_each(|(i, x)| println!("{i}:{x}")); /// ``` #[inline] #[stable(feature = "iterator_for_each", since = "1.21.0")] fn for_each(self, f: F) where Self: Sized, F: FnMut(Self::Item), { #[inline] fn call(mut f: impl FnMut(T)) -> impl FnMut((), T) { move |(), item| f(item) } self.fold((), call(f)); } /// Creates an iterator which uses a closure to determine if an element /// should be yielded. /// /// Given an element the closure must return `true` or `false`. The returned /// iterator will yield only the elements for which the closure returns /// true. /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [0i32, 1, 2]; /// /// let mut iter = a.iter().filter(|x| x.is_positive()); /// /// assert_eq!(iter.next(), Some(&1)); /// assert_eq!(iter.next(), Some(&2)); /// assert_eq!(iter.next(), None); /// ``` /// /// Because the closure passed to `filter()` takes a reference, and many /// iterators iterate over references, this leads to a possibly confusing /// situation, where the type of the closure is a double reference: /// /// ``` /// let a = [0, 1, 2]; /// /// let mut iter = a.iter().filter(|x| **x > 1); // need two *s! /// /// assert_eq!(iter.next(), Some(&2)); /// assert_eq!(iter.next(), None); /// ``` /// /// It's common to instead use destructuring on the argument to strip away /// one: /// /// ``` /// let a = [0, 1, 2]; /// /// let mut iter = a.iter().filter(|&x| *x > 1); // both & and * /// /// assert_eq!(iter.next(), Some(&2)); /// assert_eq!(iter.next(), None); /// ``` /// /// or both: /// /// ``` /// let a = [0, 1, 2]; /// /// let mut iter = a.iter().filter(|&&x| x > 1); // two &s /// /// assert_eq!(iter.next(), Some(&2)); /// assert_eq!(iter.next(), None); /// ``` /// /// of these layers. /// /// Note that `iter.filter(f).next()` is equivalent to `iter.find(f)`. #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn filter

(self, predicate: P) -> Filter where Self: Sized, P: FnMut(&Self::Item) -> bool, { Filter::new(self, predicate) } /// Creates an iterator that both filters and maps. /// /// The returned iterator yields only the `value`s for which the supplied /// closure returns `Some(value)`. /// /// `filter_map` can be used to make chains of [`filter`] and [`map`] more /// concise. The example below shows how a `map().filter().map()` can be /// shortened to a single call to `filter_map`. /// /// [`filter`]: Iterator::filter /// [`map`]: Iterator::map /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = ["1", "two", "NaN", "four", "5"]; /// /// let mut iter = a.iter().filter_map(|s| s.parse().ok()); /// /// assert_eq!(iter.next(), Some(1)); /// assert_eq!(iter.next(), Some(5)); /// assert_eq!(iter.next(), None); /// ``` /// /// Here's the same example, but with [`filter`] and [`map`]: /// /// ``` /// let a = ["1", "two", "NaN", "four", "5"]; /// let mut iter = a.iter().map(|s| s.parse()).filter(|s| s.is_ok()).map(|s| s.unwrap()); /// assert_eq!(iter.next(), Some(1)); /// assert_eq!(iter.next(), Some(5)); /// assert_eq!(iter.next(), None); /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn filter_map(self, f: F) -> FilterMap where Self: Sized, F: FnMut(Self::Item) -> Option, { FilterMap::new(self, f) } /// Creates an iterator which gives the current iteration count as well as /// the next value. /// /// The iterator returned yields pairs `(i, val)`, where `i` is the /// current index of iteration and `val` is the value returned by the /// iterator. /// /// `enumerate()` keeps its count as a [`usize`]. If you want to count by a /// different sized integer, the [`zip`] function provides similar /// functionality. /// /// # Overflow Behavior /// /// The method does no guarding against overflows, so enumerating more than /// [`usize::MAX`] elements either produces the wrong result or panics. If /// debug assertions are enabled, a panic is guaranteed. /// /// # Panics /// /// The returned iterator might panic if the to-be-returned index would /// overflow a [`usize`]. /// /// [`zip`]: Iterator::zip /// /// # Examples /// /// ``` /// let a = ['a', 'b', 'c']; /// /// let mut iter = a.iter().enumerate(); /// /// assert_eq!(iter.next(), Some((0, &'a'))); /// assert_eq!(iter.next(), Some((1, &'b'))); /// assert_eq!(iter.next(), Some((2, &'c'))); /// assert_eq!(iter.next(), None); /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn enumerate(self) -> Enumerate where Self: Sized, { Enumerate::new(self) } /// Creates an iterator which can use the [`peek`] and [`peek_mut`] methods /// to look at the next element of the iterator without consuming it. See /// their documentation for more information. /// /// Note that the underlying iterator is still advanced when [`peek`] or /// [`peek_mut`] are called for the first time: In order to retrieve the /// next element, [`next`] is called on the underlying iterator, hence any /// side effects (i.e. anything other than fetching the next value) of /// the [`next`] method will occur. /// /// /// # Examples /// /// Basic usage: /// /// ``` /// let xs = [1, 2, 3]; /// /// let mut iter = xs.iter().peekable(); /// /// // peek() lets us see into the future /// assert_eq!(iter.peek(), Some(&&1)); /// assert_eq!(iter.next(), Some(&1)); /// /// assert_eq!(iter.next(), Some(&2)); /// /// // we can peek() multiple times, the iterator won't advance /// assert_eq!(iter.peek(), Some(&&3)); /// assert_eq!(iter.peek(), Some(&&3)); /// /// assert_eq!(iter.next(), Some(&3)); /// /// // after the iterator is finished, so is peek() /// assert_eq!(iter.peek(), None); /// assert_eq!(iter.next(), None); /// ``` /// /// Using [`peek_mut`] to mutate the next item without advancing the /// iterator: /// /// ``` /// let xs = [1, 2, 3]; /// /// let mut iter = xs.iter().peekable(); /// /// // `peek_mut()` lets us see into the future /// assert_eq!(iter.peek_mut(), Some(&mut &1)); /// assert_eq!(iter.peek_mut(), Some(&mut &1)); /// assert_eq!(iter.next(), Some(&1)); /// /// if let Some(mut p) = iter.peek_mut() { /// assert_eq!(*p, &2); /// // put a value into the iterator /// *p = &1000; /// } /// /// // The value reappears as the iterator continues /// assert_eq!(iter.collect::>(), vec![&1000, &3]); /// ``` /// [`peek`]: Peekable::peek /// [`peek_mut`]: Peekable::peek_mut /// [`next`]: Iterator::next #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn peekable(self) -> Peekable where Self: Sized, { Peekable::new(self) } /// Creates an iterator that [`skip`]s elements based on a predicate. /// /// [`skip`]: Iterator::skip /// /// `skip_while()` takes a closure as an argument. It will call this /// closure on each element of the iterator, and ignore elements /// until it returns `false`. /// /// After `false` is returned, `skip_while()`'s job is over, and the /// rest of the elements are yielded. /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [-1i32, 0, 1]; /// /// let mut iter = a.iter().skip_while(|x| x.is_negative()); /// /// assert_eq!(iter.next(), Some(&0)); /// assert_eq!(iter.next(), Some(&1)); /// assert_eq!(iter.next(), None); /// ``` /// /// Because the closure passed to `skip_while()` takes a reference, and many /// iterators iterate over references, this leads to a possibly confusing /// situation, where the type of the closure argument is a double reference: /// /// ``` /// let a = [-1, 0, 1]; /// /// let mut iter = a.iter().skip_while(|x| **x < 0); // need two *s! /// /// assert_eq!(iter.next(), Some(&0)); /// assert_eq!(iter.next(), Some(&1)); /// assert_eq!(iter.next(), None); /// ``` /// /// Stopping after an initial `false`: /// /// ``` /// let a = [-1, 0, 1, -2]; /// /// let mut iter = a.iter().skip_while(|x| **x < 0); /// /// assert_eq!(iter.next(), Some(&0)); /// assert_eq!(iter.next(), Some(&1)); /// /// // while this would have been false, since we already got a false, /// // skip_while() isn't used any more /// assert_eq!(iter.next(), Some(&-2)); /// /// assert_eq!(iter.next(), None); /// ``` #[inline] #[doc(alias = "drop_while")] #[stable(feature = "rust1", since = "1.0.0")] fn skip_while

(self, predicate: P) -> SkipWhile where Self: Sized, P: FnMut(&Self::Item) -> bool, { SkipWhile::new(self, predicate) } /// Creates an iterator that yields elements based on a predicate. /// /// `take_while()` takes a closure as an argument. It will call this /// closure on each element of the iterator, and yield elements /// while it returns `true`. /// /// After `false` is returned, `take_while()`'s job is over, and the /// rest of the elements are ignored. /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [-1i32, 0, 1]; /// /// let mut iter = a.iter().take_while(|x| x.is_negative()); /// /// assert_eq!(iter.next(), Some(&-1)); /// assert_eq!(iter.next(), None); /// ``` /// /// Because the closure passed to `take_while()` takes a reference, and many /// iterators iterate over references, this leads to a possibly confusing /// situation, where the type of the closure is a double reference: /// /// ``` /// let a = [-1, 0, 1]; /// /// let mut iter = a.iter().take_while(|x| **x < 0); // need two *s! /// /// assert_eq!(iter.next(), Some(&-1)); /// assert_eq!(iter.next(), None); /// ``` /// /// Stopping after an initial `false`: /// /// ``` /// let a = [-1, 0, 1, -2]; /// /// let mut iter = a.iter().take_while(|x| **x < 0); /// /// assert_eq!(iter.next(), Some(&-1)); /// /// // We have more elements that are less than zero, but since we already /// // got a false, take_while() isn't used any more /// assert_eq!(iter.next(), None); /// ``` /// /// Because `take_while()` needs to look at the value in order to see if it /// should be included or not, consuming iterators will see that it is /// removed: /// /// ``` /// let a = [1, 2, 3, 4]; /// let mut iter = a.iter(); /// /// let result: Vec = iter.by_ref() /// .take_while(|n| **n != 3) /// .cloned() /// .collect(); /// /// assert_eq!(result, &[1, 2]); /// /// let result: Vec = iter.cloned().collect(); /// /// assert_eq!(result, &[4]); /// ``` /// /// The `3` is no longer there, because it was consumed in order to see if /// the iteration should stop, but wasn't placed back into the iterator. #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn take_while

(self, predicate: P) -> TakeWhile where Self: Sized, P: FnMut(&Self::Item) -> bool, { TakeWhile::new(self, predicate) } /// Creates an iterator that both yields elements based on a predicate and maps. /// /// `map_while()` takes a closure as an argument. It will call this /// closure on each element of the iterator, and yield elements /// while it returns [`Some(_)`][`Some`]. /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [-1i32, 4, 0, 1]; /// /// let mut iter = a.iter().map_while(|x| 16i32.checked_div(*x)); /// /// assert_eq!(iter.next(), Some(-16)); /// assert_eq!(iter.next(), Some(4)); /// assert_eq!(iter.next(), None); /// ``` /// /// Here's the same example, but with [`take_while`] and [`map`]: /// /// [`take_while`]: Iterator::take_while /// [`map`]: Iterator::map /// /// ``` /// let a = [-1i32, 4, 0, 1]; /// /// let mut iter = a.iter() /// .map(|x| 16i32.checked_div(*x)) /// .take_while(|x| x.is_some()) /// .map(|x| x.unwrap()); /// /// assert_eq!(iter.next(), Some(-16)); /// assert_eq!(iter.next(), Some(4)); /// assert_eq!(iter.next(), None); /// ``` /// /// Stopping after an initial [`None`]: /// /// ``` /// let a = [0, 1, 2, -3, 4, 5, -6]; /// /// let iter = a.iter().map_while(|x| u32::try_from(*x).ok()); /// let vec = iter.collect::>(); /// /// // We have more elements which could fit in u32 (4, 5), but `map_while` returned `None` for `-3` /// // (as the `predicate` returned `None`) and `collect` stops at the first `None` encountered. /// assert_eq!(vec, vec![0, 1, 2]); /// ``` /// /// Because `map_while()` needs to look at the value in order to see if it /// should be included or not, consuming iterators will see that it is /// removed: /// /// ``` /// let a = [1, 2, -3, 4]; /// let mut iter = a.iter(); /// /// let result: Vec = iter.by_ref() /// .map_while(|n| u32::try_from(*n).ok()) /// .collect(); /// /// assert_eq!(result, &[1, 2]); /// /// let result: Vec = iter.cloned().collect(); /// /// assert_eq!(result, &[4]); /// ``` /// /// The `-3` is no longer there, because it was consumed in order to see if /// the iteration should stop, but wasn't placed back into the iterator. /// /// Note that unlike [`take_while`] this iterator is **not** fused. /// It is also not specified what this iterator returns after the first [`None`] is returned. /// If you need fused iterator, use [`fuse`]. /// /// [`fuse`]: Iterator::fuse #[inline] #[stable(feature = "iter_map_while", since = "1.57.0")] fn map_while(self, predicate: P) -> MapWhile where Self: Sized, P: FnMut(Self::Item) -> Option, { MapWhile::new(self, predicate) } /// Creates an iterator that skips the first `n` elements. /// /// `skip(n)` skips elements until `n` elements are skipped or the end of the /// iterator is reached (whichever happens first). After that, all the remaining /// elements are yielded. In particular, if the original iterator is too short, /// then the returned iterator is empty. /// /// Rather than overriding this method directly, instead override the `nth` method. /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// /// let mut iter = a.iter().skip(2); /// /// assert_eq!(iter.next(), Some(&3)); /// assert_eq!(iter.next(), None); /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn skip(self, n: usize) -> Skip where Self: Sized, { Skip::new(self, n) } /// Creates an iterator that yields the first `n` elements, or fewer /// if the underlying iterator ends sooner. /// /// `take(n)` yields elements until `n` elements are yielded or the end of /// the iterator is reached (whichever happens first). /// The returned iterator is a prefix of length `n` if the original iterator /// contains at least `n` elements, otherwise it contains all of the /// (fewer than `n`) elements of the original iterator. /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// /// let mut iter = a.iter().take(2); /// /// assert_eq!(iter.next(), Some(&1)); /// assert_eq!(iter.next(), Some(&2)); /// assert_eq!(iter.next(), None); /// ``` /// /// `take()` is often used with an infinite iterator, to make it finite: /// /// ``` /// let mut iter = (0..).take(3); /// /// assert_eq!(iter.next(), Some(0)); /// assert_eq!(iter.next(), Some(1)); /// assert_eq!(iter.next(), Some(2)); /// assert_eq!(iter.next(), None); /// ``` /// /// If less than `n` elements are available, /// `take` will limit itself to the size of the underlying iterator: /// /// ``` /// let v = [1, 2]; /// let mut iter = v.into_iter().take(5); /// assert_eq!(iter.next(), Some(1)); /// assert_eq!(iter.next(), Some(2)); /// assert_eq!(iter.next(), None); /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn take(self, n: usize) -> Take where Self: Sized, { Take::new(self, n) } /// An iterator adapter similar to [`fold`] that holds internal state and /// produces a new iterator. /// /// [`fold`]: Iterator::fold /// /// `scan()` takes two arguments: an initial value which seeds the internal /// state, and a closure with two arguments, the first being a mutable /// reference to the internal state and the second an iterator element. /// The closure can assign to the internal state to share state between /// iterations. /// /// On iteration, the closure will be applied to each element of the /// iterator and the return value from the closure, an [`Option`], is /// yielded by the iterator. /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// /// let mut iter = a.iter().scan(1, |state, &x| { /// // each iteration, we'll multiply the state by the element /// *state = *state * x; /// /// // then, we'll yield the negation of the state /// Some(-*state) /// }); /// /// assert_eq!(iter.next(), Some(-1)); /// assert_eq!(iter.next(), Some(-2)); /// assert_eq!(iter.next(), Some(-6)); /// assert_eq!(iter.next(), None); /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn scan(self, initial_state: St, f: F) -> Scan where Self: Sized, F: FnMut(&mut St, Self::Item) -> Option, { Scan::new(self, initial_state, f) } /// Creates an iterator that works like map, but flattens nested structure. /// /// The [`map`] adapter is very useful, but only when the closure /// argument produces values. If it produces an iterator instead, there's /// an extra layer of indirection. `flat_map()` will remove this extra layer /// on its own. /// /// You can think of `flat_map(f)` as the semantic equivalent /// of [`map`]ping, and then [`flatten`]ing as in `map(f).flatten()`. /// /// Another way of thinking about `flat_map()`: [`map`]'s closure returns /// one item for each element, and `flat_map()`'s closure returns an /// iterator for each element. /// /// [`map`]: Iterator::map /// [`flatten`]: Iterator::flatten /// /// # Examples /// /// Basic usage: /// /// ``` /// let words = ["alpha", "beta", "gamma"]; /// /// // chars() returns an iterator /// let merged: String = words.iter() /// .flat_map(|s| s.chars()) /// .collect(); /// assert_eq!(merged, "alphabetagamma"); /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn flat_map(self, f: F) -> FlatMap where Self: Sized, U: IntoIterator, F: FnMut(Self::Item) -> U, { FlatMap::new(self, f) } /// Creates an iterator that flattens nested structure. /// /// This is useful when you have an iterator of iterators or an iterator of /// things that can be turned into iterators and you want to remove one /// level of indirection. /// /// # Examples /// /// Basic usage: /// /// ``` /// let data = vec![vec![1, 2, 3, 4], vec![5, 6]]; /// let flattened = data.into_iter().flatten().collect::>(); /// assert_eq!(flattened, &[1, 2, 3, 4, 5, 6]); /// ``` /// /// Mapping and then flattening: /// /// ``` /// let words = ["alpha", "beta", "gamma"]; /// /// // chars() returns an iterator /// let merged: String = words.iter() /// .map(|s| s.chars()) /// .flatten() /// .collect(); /// assert_eq!(merged, "alphabetagamma"); /// ``` /// /// You can also rewrite this in terms of [`flat_map()`], which is preferable /// in this case since it conveys intent more clearly: /// /// ``` /// let words = ["alpha", "beta", "gamma"]; /// /// // chars() returns an iterator /// let merged: String = words.iter() /// .flat_map(|s| s.chars()) /// .collect(); /// assert_eq!(merged, "alphabetagamma"); /// ``` /// /// Flattening only removes one level of nesting at a time: /// /// ``` /// let d3 = [[[1, 2], [3, 4]], [[5, 6], [7, 8]]]; /// /// let d2 = d3.iter().flatten().collect::>(); /// assert_eq!(d2, [&[1, 2], &[3, 4], &[5, 6], &[7, 8]]); /// /// let d1 = d3.iter().flatten().flatten().collect::>(); /// assert_eq!(d1, [&1, &2, &3, &4, &5, &6, &7, &8]); /// ``` /// /// Here we see that `flatten()` does not perform a "deep" flatten. /// Instead, only one level of nesting is removed. That is, if you /// `flatten()` a three-dimensional array, the result will be /// two-dimensional and not one-dimensional. To get a one-dimensional /// structure, you have to `flatten()` again. /// /// [`flat_map()`]: Iterator::flat_map #[inline] #[stable(feature = "iterator_flatten", since = "1.29.0")] fn flatten(self) -> Flatten where Self: Sized, Self::Item: IntoIterator, { Flatten::new(self) } /// Creates an iterator which ends after the first [`None`]. /// /// After an iterator returns [`None`], future calls may or may not yield /// [`Some(T)`] again. `fuse()` adapts an iterator, ensuring that after a /// [`None`] is given, it will always return [`None`] forever. /// /// Note that the [`Fuse`] wrapper is a no-op on iterators that implement /// the [`FusedIterator`] trait. `fuse()` may therefore behave incorrectly /// if the [`FusedIterator`] trait is improperly implemented. /// /// [`Some(T)`]: Some /// [`FusedIterator`]: crate::iter::FusedIterator /// /// # Examples /// /// Basic usage: /// /// ``` /// // an iterator which alternates between Some and None /// struct Alternate { /// state: i32, /// } /// /// impl Iterator for Alternate { /// type Item = i32; /// /// fn next(&mut self) -> Option { /// let val = self.state; /// self.state = self.state + 1; /// /// // if it's even, Some(i32), else None /// if val % 2 == 0 { /// Some(val) /// } else { /// None /// } /// } /// } /// /// let mut iter = Alternate { state: 0 }; /// /// // we can see our iterator going back and forth /// assert_eq!(iter.next(), Some(0)); /// assert_eq!(iter.next(), None); /// assert_eq!(iter.next(), Some(2)); /// assert_eq!(iter.next(), None); /// /// // however, once we fuse it... /// let mut iter = iter.fuse(); /// /// assert_eq!(iter.next(), Some(4)); /// assert_eq!(iter.next(), None); /// /// // it will always return `None` after the first time. /// assert_eq!(iter.next(), None); /// assert_eq!(iter.next(), None); /// assert_eq!(iter.next(), None); /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn fuse(self) -> Fuse where Self: Sized, { Fuse::new(self) } /// Does something with each element of an iterator, passing the value on. /// /// When using iterators, you'll often chain several of them together. /// While working on such code, you might want to check out what's /// happening at various parts in the pipeline. To do that, insert /// a call to `inspect()`. /// /// It's more common for `inspect()` to be used as a debugging tool than to /// exist in your final code, but applications may find it useful in certain /// situations when errors need to be logged before being discarded. /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 4, 2, 3]; /// /// // this iterator sequence is complex. /// let sum = a.iter() /// .cloned() /// .filter(|x| x % 2 == 0) /// .fold(0, |sum, i| sum + i); /// /// println!("{sum}"); /// /// // let's add some inspect() calls to investigate what's happening /// let sum = a.iter() /// .cloned() /// .inspect(|x| println!("about to filter: {x}")) /// .filter(|x| x % 2 == 0) /// .inspect(|x| println!("made it through filter: {x}")) /// .fold(0, |sum, i| sum + i); /// /// println!("{sum}"); /// ``` /// /// This will print: /// /// ```text /// 6 /// about to filter: 1 /// about to filter: 4 /// made it through filter: 4 /// about to filter: 2 /// made it through filter: 2 /// about to filter: 3 /// 6 /// ``` /// /// Logging errors before discarding them: /// /// ``` /// let lines = ["1", "2", "a"]; /// /// let sum: i32 = lines /// .iter() /// .map(|line| line.parse::()) /// .inspect(|num| { /// if let Err(ref e) = *num { /// println!("Parsing error: {e}"); /// } /// }) /// .filter_map(Result::ok) /// .sum(); /// /// println!("Sum: {sum}"); /// ``` /// /// This will print: /// /// ```text /// Parsing error: invalid digit found in string /// Sum: 3 /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn inspect(self, f: F) -> Inspect where Self: Sized, F: FnMut(&Self::Item), { Inspect::new(self, f) } /// Borrows an iterator, rather than consuming it. /// /// This is useful to allow applying iterator adapters while still /// retaining ownership of the original iterator. /// /// # Examples /// /// Basic usage: /// /// ``` /// let mut words = ["hello", "world", "of", "Rust"].into_iter(); /// /// // Take the first two words. /// let hello_world: Vec<_> = words.by_ref().take(2).collect(); /// assert_eq!(hello_world, vec!["hello", "world"]); /// /// // Collect the rest of the words. /// // We can only do this because we used `by_ref` earlier. /// let of_rust: Vec<_> = words.collect(); /// assert_eq!(of_rust, vec!["of", "Rust"]); /// ``` #[stable(feature = "rust1", since = "1.0.0")] fn by_ref(&mut self) -> &mut Self where Self: Sized, { self } /// Transforms an iterator into a collection. /// /// `collect()` can take anything iterable, and turn it into a relevant /// collection. This is one of the more powerful methods in the standard /// library, used in a variety of contexts. /// /// The most basic pattern in which `collect()` is used is to turn one /// collection into another. You take a collection, call [`iter`] on it, /// do a bunch of transformations, and then `collect()` at the end. /// /// `collect()` can also create instances of types that are not typical /// collections. For example, a [`String`] can be built from [`char`]s, /// and an iterator of [`Result`][`Result`] items can be collected /// into `Result, E>`. See the examples below for more. /// /// Because `collect()` is so general, it can cause problems with type /// inference. As such, `collect()` is one of the few times you'll see /// the syntax affectionately known as the 'turbofish': `::<>`. This /// helps the inference algorithm understand specifically which collection /// you're trying to collect into. /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// /// let doubled: Vec = a.iter() /// .map(|&x| x * 2) /// .collect(); /// /// assert_eq!(vec![2, 4, 6], doubled); /// ``` /// /// Note that we needed the `: Vec` on the left-hand side. This is because /// we could collect into, for example, a [`VecDeque`] instead: /// /// [`VecDeque`]: ../../std/collections/struct.VecDeque.html /// /// ``` /// use std::collections::VecDeque; /// /// let a = [1, 2, 3]; /// /// let doubled: VecDeque = a.iter().map(|&x| x * 2).collect(); /// /// assert_eq!(2, doubled[0]); /// assert_eq!(4, doubled[1]); /// assert_eq!(6, doubled[2]); /// ``` /// /// Using the 'turbofish' instead of annotating `doubled`: /// /// ``` /// let a = [1, 2, 3]; /// /// let doubled = a.iter().map(|x| x * 2).collect::>(); /// /// assert_eq!(vec![2, 4, 6], doubled); /// ``` /// /// Because `collect()` only cares about what you're collecting into, you can /// still use a partial type hint, `_`, with the turbofish: /// /// ``` /// let a = [1, 2, 3]; /// /// let doubled = a.iter().map(|x| x * 2).collect::>(); /// /// assert_eq!(vec![2, 4, 6], doubled); /// ``` /// /// Using `collect()` to make a [`String`]: /// /// ``` /// let chars = ['g', 'd', 'k', 'k', 'n']; /// /// let hello: String = chars.iter() /// .map(|&x| x as u8) /// .map(|x| (x + 1) as char) /// .collect(); /// /// assert_eq!("hello", hello); /// ``` /// /// If you have a list of [`Result`][`Result`]s, you can use `collect()` to /// see if any of them failed: /// /// ``` /// let results = [Ok(1), Err("nope"), Ok(3), Err("bad")]; /// /// let result: Result, &str> = results.iter().cloned().collect(); /// /// // gives us the first error /// assert_eq!(Err("nope"), result); /// /// let results = [Ok(1), Ok(3)]; /// /// let result: Result, &str> = results.iter().cloned().collect(); /// /// // gives us the list of answers /// assert_eq!(Ok(vec![1, 3]), result); /// ``` /// /// [`iter`]: Iterator::next /// [`String`]: ../../std/string/struct.String.html /// [`char`]: type@char #[inline] #[stable(feature = "rust1", since = "1.0.0")] #[must_use = "if you really need to exhaust the iterator, consider `.for_each(drop)` instead"] fn collect>(self) -> B where Self: Sized, { FromIterator::from_iter(self) } /// Fallibly transforms an iterator into a collection, short circuiting if /// a failure is encountered. /// /// `try_collect()` is a variation of [`collect()`][`collect`] that allows fallible /// conversions during collection. Its main use case is simplifying conversions from /// iterators yielding [`Option`][`Option`] into `Option>`, or similarly for other [`Try`] /// types (e.g. [`Result`]). /// /// Importantly, `try_collect()` doesn't require that the outer [`Try`] type also implements [`FromIterator`]; /// only the inner type produced on `Try::Output` must implement it. Concretely, /// this means that collecting into `ControlFlow<_, Vec>` is valid because `Vec` implements /// [`FromIterator`], even though [`ControlFlow`] doesn't. /// /// Also, if a failure is encountered during `try_collect()`, the iterator is still valid and /// may continue to be used, in which case it will continue iterating starting after the element that /// triggered the failure. See the last example below for an example of how this works. /// /// # Examples /// Successfully collecting an iterator of `Option` into `Option>`: /// ``` /// #![feature(iterator_try_collect)] /// /// let u = vec![Some(1), Some(2), Some(3)]; /// let v = u.into_iter().try_collect::>(); /// assert_eq!(v, Some(vec![1, 2, 3])); /// ``` /// /// Failing to collect in the same way: /// ``` /// #![feature(iterator_try_collect)] /// /// let u = vec![Some(1), Some(2), None, Some(3)]; /// let v = u.into_iter().try_collect::>(); /// assert_eq!(v, None); /// ``` /// /// A similar example, but with `Result`: /// ``` /// #![feature(iterator_try_collect)] /// /// let u: Vec> = vec![Ok(1), Ok(2), Ok(3)]; /// let v = u.into_iter().try_collect::>(); /// assert_eq!(v, Ok(vec![1, 2, 3])); /// /// let u = vec![Ok(1), Ok(2), Err(()), Ok(3)]; /// let v = u.into_iter().try_collect::>(); /// assert_eq!(v, Err(())); /// ``` /// /// Finally, even [`ControlFlow`] works, despite the fact that it /// doesn't implement [`FromIterator`]. Note also that the iterator can /// continue to be used, even if a failure is encountered: /// /// ``` /// #![feature(iterator_try_collect)] /// /// use core::ops::ControlFlow::{Break, Continue}; /// /// let u = [Continue(1), Continue(2), Break(3), Continue(4), Continue(5)]; /// let mut it = u.into_iter(); /// /// let v = it.try_collect::>(); /// assert_eq!(v, Break(3)); /// /// let v = it.try_collect::>(); /// assert_eq!(v, Continue(vec![4, 5])); /// ``` /// /// [`collect`]: Iterator::collect #[inline] #[unstable(feature = "iterator_try_collect", issue = "94047")] fn try_collect(&mut self) -> ChangeOutputType where Self: Sized, ::Item: Try, <::Item as Try>::Residual: Residual, B: FromIterator<::Output>, { try_process(ByRefSized(self), |i| i.collect()) } /// Collects all the items from an iterator into a collection. /// /// This method consumes the iterator and adds all its items to the /// passed collection. The collection is then returned, so the call chain /// can be continued. /// /// This is useful when you already have a collection and wants to add /// the iterator items to it. /// /// This method is a convenience method to call [Extend::extend](trait.Extend.html), /// but instead of being called on a collection, it's called on an iterator. /// /// # Examples /// /// Basic usage: /// /// ``` /// #![feature(iter_collect_into)] /// /// let a = [1, 2, 3]; /// let mut vec: Vec:: = vec![0, 1]; /// /// a.iter().map(|&x| x * 2).collect_into(&mut vec); /// a.iter().map(|&x| x * 10).collect_into(&mut vec); /// /// assert_eq!(vec![0, 1, 2, 4, 6, 10, 20, 30], vec); /// ``` /// /// `Vec` can have a manual set capacity to avoid reallocating it: /// /// ``` /// #![feature(iter_collect_into)] /// /// let a = [1, 2, 3]; /// let mut vec: Vec:: = Vec::with_capacity(6); /// /// a.iter().map(|&x| x * 2).collect_into(&mut vec); /// a.iter().map(|&x| x * 10).collect_into(&mut vec); /// /// assert_eq!(6, vec.capacity()); /// println!("{:?}", vec); /// ``` /// /// The returned mutable reference can be used to continue the call chain: /// /// ``` /// #![feature(iter_collect_into)] /// /// let a = [1, 2, 3]; /// let mut vec: Vec:: = Vec::with_capacity(6); /// /// let count = a.iter().collect_into(&mut vec).iter().count(); /// /// assert_eq!(count, vec.len()); /// println!("Vec len is {}", count); /// /// let count = a.iter().collect_into(&mut vec).iter().count(); /// /// assert_eq!(count, vec.len()); /// println!("Vec len now is {}", count); /// ``` #[inline] #[unstable(feature = "iter_collect_into", reason = "new API", issue = "94780")] fn collect_into>(self, collection: &mut E) -> &mut E where Self: Sized, { collection.extend(self); collection } /// Consumes an iterator, creating two collections from it. /// /// The predicate passed to `partition()` can return `true`, or `false`. /// `partition()` returns a pair, all of the elements for which it returned /// `true`, and all of the elements for which it returned `false`. /// /// See also [`is_partitioned()`] and [`partition_in_place()`]. /// /// [`is_partitioned()`]: Iterator::is_partitioned /// [`partition_in_place()`]: Iterator::partition_in_place /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// /// let (even, odd): (Vec<_>, Vec<_>) = a /// .into_iter() /// .partition(|n| n % 2 == 0); /// /// assert_eq!(even, vec![2]); /// assert_eq!(odd, vec![1, 3]); /// ``` #[stable(feature = "rust1", since = "1.0.0")] fn partition(self, f: F) -> (B, B) where Self: Sized, B: Default + Extend, F: FnMut(&Self::Item) -> bool, { #[inline] fn extend<'a, T, B: Extend>( mut f: impl FnMut(&T) -> bool + 'a, left: &'a mut B, right: &'a mut B, ) -> impl FnMut((), T) + 'a { move |(), x| { if f(&x) { left.extend_one(x); } else { right.extend_one(x); } } } let mut left: B = Default::default(); let mut right: B = Default::default(); self.fold((), extend(f, &mut left, &mut right)); (left, right) } /// Reorders the elements of this iterator *in-place* according to the given predicate, /// such that all those that return `true` precede all those that return `false`. /// Returns the number of `true` elements found. /// /// The relative order of partitioned items is not maintained. /// /// # Current implementation /// /// Current algorithms tries finding the first element for which the predicate evaluates /// to false, and the last element for which it evaluates to true and repeatedly swaps them. /// /// Time complexity: *O*(*n*) /// /// See also [`is_partitioned()`] and [`partition()`]. /// /// [`is_partitioned()`]: Iterator::is_partitioned /// [`partition()`]: Iterator::partition /// /// # Examples /// /// ``` /// #![feature(iter_partition_in_place)] /// /// let mut a = [1, 2, 3, 4, 5, 6, 7]; /// /// // Partition in-place between evens and odds /// let i = a.iter_mut().partition_in_place(|&n| n % 2 == 0); /// /// assert_eq!(i, 3); /// assert!(a[..i].iter().all(|&n| n % 2 == 0)); // evens /// assert!(a[i..].iter().all(|&n| n % 2 == 1)); // odds /// ``` #[unstable(feature = "iter_partition_in_place", reason = "new API", issue = "62543")] fn partition_in_place<'a, T: 'a, P>(mut self, ref mut predicate: P) -> usize where Self: Sized + DoubleEndedIterator, P: FnMut(&T) -> bool, { // FIXME: should we worry about the count overflowing? The only way to have more than // `usize::MAX` mutable references is with ZSTs, which aren't useful to partition... // These closure "factory" functions exist to avoid genericity in `Self`. #[inline] fn is_false<'a, T>( predicate: &'a mut impl FnMut(&T) -> bool, true_count: &'a mut usize, ) -> impl FnMut(&&mut T) -> bool + 'a { move |x| { let p = predicate(&**x); *true_count += p as usize; !p } } #[inline] fn is_true(predicate: &mut impl FnMut(&T) -> bool) -> impl FnMut(&&mut T) -> bool + '_ { move |x| predicate(&**x) } // Repeatedly find the first `false` and swap it with the last `true`. let mut true_count = 0; while let Some(head) = self.find(is_false(predicate, &mut true_count)) { if let Some(tail) = self.rfind(is_true(predicate)) { crate::mem::swap(head, tail); true_count += 1; } else { break; } } true_count } /// Checks if the elements of this iterator are partitioned according to the given predicate, /// such that all those that return `true` precede all those that return `false`. /// /// See also [`partition()`] and [`partition_in_place()`]. /// /// [`partition()`]: Iterator::partition /// [`partition_in_place()`]: Iterator::partition_in_place /// /// # Examples /// /// ``` /// #![feature(iter_is_partitioned)] /// /// assert!("Iterator".chars().is_partitioned(char::is_uppercase)); /// assert!(!"IntoIterator".chars().is_partitioned(char::is_uppercase)); /// ``` #[unstable(feature = "iter_is_partitioned", reason = "new API", issue = "62544")] fn is_partitioned

(mut self, mut predicate: P) -> bool where Self: Sized, P: FnMut(Self::Item) -> bool, { // Either all items test `true`, or the first clause stops at `false` // and we check that there are no more `true` items after that. self.all(&mut predicate) || !self.any(predicate) } /// An iterator method that applies a function as long as it returns /// successfully, producing a single, final value. /// /// `try_fold()` takes two arguments: an initial value, and a closure with /// two arguments: an 'accumulator', and an element. The closure either /// returns successfully, with the value that the accumulator should have /// for the next iteration, or it returns failure, with an error value that /// is propagated back to the caller immediately (short-circuiting). /// /// The initial value is the value the accumulator will have on the first /// call. If applying the closure succeeded against every element of the /// iterator, `try_fold()` returns the final accumulator as success. /// /// Folding is useful whenever you have a collection of something, and want /// to produce a single value from it. /// /// # Note to Implementors /// /// Several of the other (forward) methods have default implementations in /// terms of this one, so try to implement this explicitly if it can /// do something better than the default `for` loop implementation. /// /// In particular, try to have this call `try_fold()` on the internal parts /// from which this iterator is composed. If multiple calls are needed, /// the `?` operator may be convenient for chaining the accumulator value /// along, but beware any invariants that need to be upheld before those /// early returns. This is a `&mut self` method, so iteration needs to be /// resumable after hitting an error here. /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// /// // the checked sum of all of the elements of the array /// let sum = a.iter().try_fold(0i8, |acc, &x| acc.checked_add(x)); /// /// assert_eq!(sum, Some(6)); /// ``` /// /// Short-circuiting: /// /// ``` /// let a = [10, 20, 30, 100, 40, 50]; /// let mut it = a.iter(); /// /// // This sum overflows when adding the 100 element /// let sum = it.try_fold(0i8, |acc, &x| acc.checked_add(x)); /// assert_eq!(sum, None); /// /// // Because it short-circuited, the remaining elements are still /// // available through the iterator. /// assert_eq!(it.len(), 2); /// assert_eq!(it.next(), Some(&40)); /// ``` /// /// While you cannot `break` from a closure, the [`ControlFlow`] type allows /// a similar idea: /// /// ``` /// use std::ops::ControlFlow; /// /// let triangular = (1..30).try_fold(0_i8, |prev, x| { /// if let Some(next) = prev.checked_add(x) { /// ControlFlow::Continue(next) /// } else { /// ControlFlow::Break(prev) /// } /// }); /// assert_eq!(triangular, ControlFlow::Break(120)); /// /// let triangular = (1..30).try_fold(0_u64, |prev, x| { /// if let Some(next) = prev.checked_add(x) { /// ControlFlow::Continue(next) /// } else { /// ControlFlow::Break(prev) /// } /// }); /// assert_eq!(triangular, ControlFlow::Continue(435)); /// ``` #[inline] #[stable(feature = "iterator_try_fold", since = "1.27.0")] fn try_fold(&mut self, init: B, mut f: F) -> R where Self: Sized, F: FnMut(B, Self::Item) -> R, R: Try, { let mut accum = init; while let Some(x) = self.next() { accum = f(accum, x)?; } try { accum } } /// An iterator method that applies a fallible function to each item in the /// iterator, stopping at the first error and returning that error. /// /// This can also be thought of as the fallible form of [`for_each()`] /// or as the stateless version of [`try_fold()`]. /// /// [`for_each()`]: Iterator::for_each /// [`try_fold()`]: Iterator::try_fold /// /// # Examples /// /// ``` /// use std::fs::rename; /// use std::io::{stdout, Write}; /// use std::path::Path; /// /// let data = ["no_tea.txt", "stale_bread.json", "torrential_rain.png"]; /// /// let res = data.iter().try_for_each(|x| writeln!(stdout(), "{x}")); /// assert!(res.is_ok()); /// /// let mut it = data.iter().cloned(); /// let res = it.try_for_each(|x| rename(x, Path::new(x).with_extension("old"))); /// assert!(res.is_err()); /// // It short-circuited, so the remaining items are still in the iterator: /// assert_eq!(it.next(), Some("stale_bread.json")); /// ``` /// /// The [`ControlFlow`] type can be used with this method for the situations /// in which you'd use `break` and `continue` in a normal loop: /// /// ``` /// use std::ops::ControlFlow; /// /// let r = (2..100).try_for_each(|x| { /// if 323 % x == 0 { /// return ControlFlow::Break(x) /// } /// /// ControlFlow::Continue(()) /// }); /// assert_eq!(r, ControlFlow::Break(17)); /// ``` #[inline] #[stable(feature = "iterator_try_fold", since = "1.27.0")] fn try_for_each(&mut self, f: F) -> R where Self: Sized, F: FnMut(Self::Item) -> R, R: Try, { #[inline] fn call(mut f: impl FnMut(T) -> R) -> impl FnMut((), T) -> R { move |(), x| f(x) } self.try_fold((), call(f)) } /// Folds every element into an accumulator by applying an operation, /// returning the final result. /// /// `fold()` takes two arguments: an initial value, and a closure with two /// arguments: an 'accumulator', and an element. The closure returns the value that /// the accumulator should have for the next iteration. /// /// The initial value is the value the accumulator will have on the first /// call. /// /// After applying this closure to every element of the iterator, `fold()` /// returns the accumulator. /// /// This operation is sometimes called 'reduce' or 'inject'. /// /// Folding is useful whenever you have a collection of something, and want /// to produce a single value from it. /// /// Note: `fold()`, and similar methods that traverse the entire iterator, /// might not terminate for infinite iterators, even on traits for which a /// result is determinable in finite time. /// /// Note: [`reduce()`] can be used to use the first element as the initial /// value, if the accumulator type and item type is the same. /// /// Note: `fold()` combines elements in a *left-associative* fashion. For associative /// operators like `+`, the order the elements are combined in is not important, but for non-associative /// operators like `-` the order will affect the final result. /// For a *right-associative* version of `fold()`, see [`DoubleEndedIterator::rfold()`]. /// /// # Note to Implementors /// /// Several of the other (forward) methods have default implementations in /// terms of this one, so try to implement this explicitly if it can /// do something better than the default `for` loop implementation. /// /// In particular, try to have this call `fold()` on the internal parts /// from which this iterator is composed. /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// /// // the sum of all of the elements of the array /// let sum = a.iter().fold(0, |acc, x| acc + x); /// /// assert_eq!(sum, 6); /// ``` /// /// Let's walk through each step of the iteration here: /// /// | element | acc | x | result | /// |---------|-----|---|--------| /// | | 0 | | | /// | 1 | 0 | 1 | 1 | /// | 2 | 1 | 2 | 3 | /// | 3 | 3 | 3 | 6 | /// /// And so, our final result, `6`. /// /// This example demonstrates the left-associative nature of `fold()`: /// it builds a string, starting with an initial value /// and continuing with each element from the front until the back: /// /// ``` /// let numbers = [1, 2, 3, 4, 5]; /// /// let zero = "0".to_string(); /// /// let result = numbers.iter().fold(zero, |acc, &x| { /// format!("({acc} + {x})") /// }); /// /// assert_eq!(result, "(((((0 + 1) + 2) + 3) + 4) + 5)"); /// ``` /// It's common for people who haven't used iterators a lot to /// use a `for` loop with a list of things to build up a result. Those /// can be turned into `fold()`s: /// /// [`for`]: ../../book/ch03-05-control-flow.html#looping-through-a-collection-with-for /// /// ``` /// let numbers = [1, 2, 3, 4, 5]; /// /// let mut result = 0; /// /// // for loop: /// for i in &numbers { /// result = result + i; /// } /// /// // fold: /// let result2 = numbers.iter().fold(0, |acc, &x| acc + x); /// /// // they're the same /// assert_eq!(result, result2); /// ``` /// /// [`reduce()`]: Iterator::reduce #[doc(alias = "inject", alias = "foldl")] #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn fold(mut self, init: B, mut f: F) -> B where Self: Sized, F: FnMut(B, Self::Item) -> B, { let mut accum = init; while let Some(x) = self.next() { accum = f(accum, x); } accum } /// Reduces the elements to a single one, by repeatedly applying a reducing /// operation. /// /// If the iterator is empty, returns [`None`]; otherwise, returns the /// result of the reduction. /// /// The reducing function is a closure with two arguments: an 'accumulator', and an element. /// For iterators with at least one element, this is the same as [`fold()`] /// with the first element of the iterator as the initial accumulator value, folding /// every subsequent element into it. /// /// [`fold()`]: Iterator::fold /// /// # Example /// /// Find the maximum value: /// /// ``` /// fn find_max(iter: I) -> Option /// where I: Iterator, /// I::Item: Ord, /// { /// iter.reduce(|accum, item| { /// if accum >= item { accum } else { item } /// }) /// } /// let a = [10, 20, 5, -23, 0]; /// let b: [u32; 0] = []; /// /// assert_eq!(find_max(a.iter()), Some(&20)); /// assert_eq!(find_max(b.iter()), None); /// ``` #[inline] #[stable(feature = "iterator_fold_self", since = "1.51.0")] fn reduce(mut self, f: F) -> Option where Self: Sized, F: FnMut(Self::Item, Self::Item) -> Self::Item, { let first = self.next()?; Some(self.fold(first, f)) } /// Reduces the elements to a single one by repeatedly applying a reducing operation. If the /// closure returns a failure, the failure is propagated back to the caller immediately. /// /// The return type of this method depends on the return type of the closure. If the closure /// returns `Result`, then this function will return `Result, /// E>`. If the closure returns `Option`, then this function will return /// `Option>`. /// /// When called on an empty iterator, this function will return either `Some(None)` or /// `Ok(None)` depending on the type of the provided closure. /// /// For iterators with at least one element, this is essentially the same as calling /// [`try_fold()`] with the first element of the iterator as the initial accumulator value. /// /// [`try_fold()`]: Iterator::try_fold /// /// # Examples /// /// Safely calculate the sum of a series of numbers: /// /// ``` /// #![feature(iterator_try_reduce)] /// /// let numbers: Vec = vec![10, 20, 5, 23, 0]; /// let sum = numbers.into_iter().try_reduce(|x, y| x.checked_add(y)); /// assert_eq!(sum, Some(Some(58))); /// ``` /// /// Determine when a reduction short circuited: /// /// ``` /// #![feature(iterator_try_reduce)] /// /// let numbers = vec![1, 2, 3, usize::MAX, 4, 5]; /// let sum = numbers.into_iter().try_reduce(|x, y| x.checked_add(y)); /// assert_eq!(sum, None); /// ``` /// /// Determine when a reduction was not performed because there are no elements: /// /// ``` /// #![feature(iterator_try_reduce)] /// /// let numbers: Vec = Vec::new(); /// let sum = numbers.into_iter().try_reduce(|x, y| x.checked_add(y)); /// assert_eq!(sum, Some(None)); /// ``` /// /// Use a [`Result`] instead of an [`Option`]: /// /// ``` /// #![feature(iterator_try_reduce)] /// /// let numbers = vec!["1", "2", "3", "4", "5"]; /// let max: Result, ::Err> = /// numbers.into_iter().try_reduce(|x, y| { /// if x.parse::()? > y.parse::()? { Ok(x) } else { Ok(y) } /// }); /// assert_eq!(max, Ok(Some("5"))); /// ``` #[inline] #[unstable(feature = "iterator_try_reduce", reason = "new API", issue = "87053")] fn try_reduce(&mut self, f: F) -> ChangeOutputType> where Self: Sized, F: FnMut(Self::Item, Self::Item) -> R, R: Try, R::Residual: Residual>, { let first = match self.next() { Some(i) => i, None => return Try::from_output(None), }; match self.try_fold(first, f).branch() { ControlFlow::Break(r) => FromResidual::from_residual(r), ControlFlow::Continue(i) => Try::from_output(Some(i)), } } /// Tests if every element of the iterator matches a predicate. /// /// `all()` takes a closure that returns `true` or `false`. It applies /// this closure to each element of the iterator, and if they all return /// `true`, then so does `all()`. If any of them return `false`, it /// returns `false`. /// /// `all()` is short-circuiting; in other words, it will stop processing /// as soon as it finds a `false`, given that no matter what else happens, /// the result will also be `false`. /// /// An empty iterator returns `true`. /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// /// assert!(a.iter().all(|&x| x > 0)); /// /// assert!(!a.iter().all(|&x| x > 2)); /// ``` /// /// Stopping at the first `false`: /// /// ``` /// let a = [1, 2, 3]; /// /// let mut iter = a.iter(); /// /// assert!(!iter.all(|&x| x != 2)); /// /// // we can still use `iter`, as there are more elements. /// assert_eq!(iter.next(), Some(&3)); /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn all(&mut self, f: F) -> bool where Self: Sized, F: FnMut(Self::Item) -> bool, { #[inline] fn check(mut f: impl FnMut(T) -> bool) -> impl FnMut((), T) -> ControlFlow<()> { move |(), x| { if f(x) { ControlFlow::CONTINUE } else { ControlFlow::BREAK } } } self.try_fold((), check(f)) == ControlFlow::CONTINUE } /// Tests if any element of the iterator matches a predicate. /// /// `any()` takes a closure that returns `true` or `false`. It applies /// this closure to each element of the iterator, and if any of them return /// `true`, then so does `any()`. If they all return `false`, it /// returns `false`. /// /// `any()` is short-circuiting; in other words, it will stop processing /// as soon as it finds a `true`, given that no matter what else happens, /// the result will also be `true`. /// /// An empty iterator returns `false`. /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// /// assert!(a.iter().any(|&x| x > 0)); /// /// assert!(!a.iter().any(|&x| x > 5)); /// ``` /// /// Stopping at the first `true`: /// /// ``` /// let a = [1, 2, 3]; /// /// let mut iter = a.iter(); /// /// assert!(iter.any(|&x| x != 2)); /// /// // we can still use `iter`, as there are more elements. /// assert_eq!(iter.next(), Some(&2)); /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn any(&mut self, f: F) -> bool where Self: Sized, F: FnMut(Self::Item) -> bool, { #[inline] fn check(mut f: impl FnMut(T) -> bool) -> impl FnMut((), T) -> ControlFlow<()> { move |(), x| { if f(x) { ControlFlow::BREAK } else { ControlFlow::CONTINUE } } } self.try_fold((), check(f)) == ControlFlow::BREAK } /// Searches for an element of an iterator that satisfies a predicate. /// /// `find()` takes a closure that returns `true` or `false`. It applies /// this closure to each element of the iterator, and if any of them return /// `true`, then `find()` returns [`Some(element)`]. If they all return /// `false`, it returns [`None`]. /// /// `find()` is short-circuiting; in other words, it will stop processing /// as soon as the closure returns `true`. /// /// Because `find()` takes a reference, and many iterators iterate over /// references, this leads to a possibly confusing situation where the /// argument is a double reference. You can see this effect in the /// examples below, with `&&x`. /// /// [`Some(element)`]: Some /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// /// assert_eq!(a.iter().find(|&&x| x == 2), Some(&2)); /// /// assert_eq!(a.iter().find(|&&x| x == 5), None); /// ``` /// /// Stopping at the first `true`: /// /// ``` /// let a = [1, 2, 3]; /// /// let mut iter = a.iter(); /// /// assert_eq!(iter.find(|&&x| x == 2), Some(&2)); /// /// // we can still use `iter`, as there are more elements. /// assert_eq!(iter.next(), Some(&3)); /// ``` /// /// Note that `iter.find(f)` is equivalent to `iter.filter(f).next()`. #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn find

(&mut self, predicate: P) -> Option where Self: Sized, P: FnMut(&Self::Item) -> bool, { #[inline] fn check(mut predicate: impl FnMut(&T) -> bool) -> impl FnMut((), T) -> ControlFlow { move |(), x| { if predicate(&x) { ControlFlow::Break(x) } else { ControlFlow::CONTINUE } } } self.try_fold((), check(predicate)).break_value() } /// Applies function to the elements of iterator and returns /// the first non-none result. /// /// `iter.find_map(f)` is equivalent to `iter.filter_map(f).next()`. /// /// # Examples /// /// ``` /// let a = ["lol", "NaN", "2", "5"]; /// /// let first_number = a.iter().find_map(|s| s.parse().ok()); /// /// assert_eq!(first_number, Some(2)); /// ``` #[inline] #[stable(feature = "iterator_find_map", since = "1.30.0")] fn find_map(&mut self, f: F) -> Option where Self: Sized, F: FnMut(Self::Item) -> Option, { #[inline] fn check(mut f: impl FnMut(T) -> Option) -> impl FnMut((), T) -> ControlFlow { move |(), x| match f(x) { Some(x) => ControlFlow::Break(x), None => ControlFlow::CONTINUE, } } self.try_fold((), check(f)).break_value() } /// Applies function to the elements of iterator and returns /// the first true result or the first error. /// /// The return type of this method depends on the return type of the closure. /// If you return `Result` from the closure, you'll get a `Result; E>`. /// If you return `Option` from the closure, you'll get an `Option>`. /// /// # Examples /// /// ``` /// #![feature(try_find)] /// /// let a = ["1", "2", "lol", "NaN", "5"]; /// /// let is_my_num = |s: &str, search: i32| -> Result { /// Ok(s.parse::()? == search) /// }; /// /// let result = a.iter().try_find(|&&s| is_my_num(s, 2)); /// assert_eq!(result, Ok(Some(&"2"))); /// /// let result = a.iter().try_find(|&&s| is_my_num(s, 5)); /// assert!(result.is_err()); /// ``` /// /// This also supports other types which implement `Try`, not just `Result`. /// ``` /// #![feature(try_find)] /// /// use std::num::NonZeroU32; /// let a = [3, 5, 7, 4, 9, 0, 11]; /// let result = a.iter().try_find(|&&x| NonZeroU32::new(x).map(|y| y.is_power_of_two())); /// assert_eq!(result, Some(Some(&4))); /// let result = a.iter().take(3).try_find(|&&x| NonZeroU32::new(x).map(|y| y.is_power_of_two())); /// assert_eq!(result, Some(None)); /// let result = a.iter().rev().try_find(|&&x| NonZeroU32::new(x).map(|y| y.is_power_of_two())); /// assert_eq!(result, None); /// ``` #[inline] #[unstable(feature = "try_find", reason = "new API", issue = "63178")] fn try_find(&mut self, f: F) -> ChangeOutputType> where Self: Sized, F: FnMut(&Self::Item) -> R, R: Try, R::Residual: Residual>, { #[inline] fn check( mut f: impl FnMut(&I) -> V, ) -> impl FnMut((), I) -> ControlFlow where V: Try, R: Residual>, { move |(), x| match f(&x).branch() { ControlFlow::Continue(false) => ControlFlow::CONTINUE, ControlFlow::Continue(true) => ControlFlow::Break(Try::from_output(Some(x))), ControlFlow::Break(r) => ControlFlow::Break(FromResidual::from_residual(r)), } } match self.try_fold((), check(f)) { ControlFlow::Break(x) => x, ControlFlow::Continue(()) => Try::from_output(None), } } /// Searches for an element in an iterator, returning its index. /// /// `position()` takes a closure that returns `true` or `false`. It applies /// this closure to each element of the iterator, and if one of them /// returns `true`, then `position()` returns [`Some(index)`]. If all of /// them return `false`, it returns [`None`]. /// /// `position()` is short-circuiting; in other words, it will stop /// processing as soon as it finds a `true`. /// /// # Overflow Behavior /// /// The method does no guarding against overflows, so if there are more /// than [`usize::MAX`] non-matching elements, it either produces the wrong /// result or panics. If debug assertions are enabled, a panic is /// guaranteed. /// /// # Panics /// /// This function might panic if the iterator has more than `usize::MAX` /// non-matching elements. /// /// [`Some(index)`]: Some /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// /// assert_eq!(a.iter().position(|&x| x == 2), Some(1)); /// /// assert_eq!(a.iter().position(|&x| x == 5), None); /// ``` /// /// Stopping at the first `true`: /// /// ``` /// let a = [1, 2, 3, 4]; /// /// let mut iter = a.iter(); /// /// assert_eq!(iter.position(|&x| x >= 2), Some(1)); /// /// // we can still use `iter`, as there are more elements. /// assert_eq!(iter.next(), Some(&3)); /// /// // The returned index depends on iterator state /// assert_eq!(iter.position(|&x| x == 4), Some(0)); /// /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn position

(&mut self, predicate: P) -> Option where Self: Sized, P: FnMut(Self::Item) -> bool, { #[inline] fn check( mut predicate: impl FnMut(T) -> bool, ) -> impl FnMut(usize, T) -> ControlFlow { #[rustc_inherit_overflow_checks] move |i, x| { if predicate(x) { ControlFlow::Break(i) } else { ControlFlow::Continue(i + 1) } } } self.try_fold(0, check(predicate)).break_value() } /// Searches for an element in an iterator from the right, returning its /// index. /// /// `rposition()` takes a closure that returns `true` or `false`. It applies /// this closure to each element of the iterator, starting from the end, /// and if one of them returns `true`, then `rposition()` returns /// [`Some(index)`]. If all of them return `false`, it returns [`None`]. /// /// `rposition()` is short-circuiting; in other words, it will stop /// processing as soon as it finds a `true`. /// /// [`Some(index)`]: Some /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// /// assert_eq!(a.iter().rposition(|&x| x == 3), Some(2)); /// /// assert_eq!(a.iter().rposition(|&x| x == 5), None); /// ``` /// /// Stopping at the first `true`: /// /// ``` /// let a = [1, 2, 3]; /// /// let mut iter = a.iter(); /// /// assert_eq!(iter.rposition(|&x| x == 2), Some(1)); /// /// // we can still use `iter`, as there are more elements. /// assert_eq!(iter.next(), Some(&1)); /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn rposition

(&mut self, predicate: P) -> Option where P: FnMut(Self::Item) -> bool, Self: Sized + ExactSizeIterator + DoubleEndedIterator, { // No need for an overflow check here, because `ExactSizeIterator` // implies that the number of elements fits into a `usize`. #[inline] fn check( mut predicate: impl FnMut(T) -> bool, ) -> impl FnMut(usize, T) -> ControlFlow { move |i, x| { let i = i - 1; if predicate(x) { ControlFlow::Break(i) } else { ControlFlow::Continue(i) } } } let n = self.len(); self.try_rfold(n, check(predicate)).break_value() } /// Returns the maximum element of an iterator. /// /// If several elements are equally maximum, the last element is /// returned. If the iterator is empty, [`None`] is returned. /// /// Note that [`f32`]/[`f64`] doesn't implement [`Ord`] due to NaN being /// incomparable. You can work around this by using [`Iterator::reduce`]: /// ``` /// assert_eq!( /// [2.4, f32::NAN, 1.3] /// .into_iter() /// .reduce(f32::max) /// .unwrap(), /// 2.4 /// ); /// ``` /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// let b: Vec = Vec::new(); /// /// assert_eq!(a.iter().max(), Some(&3)); /// assert_eq!(b.iter().max(), None); /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn max(self) -> Option where Self: Sized, Self::Item: Ord, { self.max_by(Ord::cmp) } /// Returns the minimum element of an iterator. /// /// If several elements are equally minimum, the first element is returned. /// If the iterator is empty, [`None`] is returned. /// /// Note that [`f32`]/[`f64`] doesn't implement [`Ord`] due to NaN being /// incomparable. You can work around this by using [`Iterator::reduce`]: /// ``` /// assert_eq!( /// [2.4, f32::NAN, 1.3] /// .into_iter() /// .reduce(f32::min) /// .unwrap(), /// 1.3 /// ); /// ``` /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// let b: Vec = Vec::new(); /// /// assert_eq!(a.iter().min(), Some(&1)); /// assert_eq!(b.iter().min(), None); /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] fn min(self) -> Option where Self: Sized, Self::Item: Ord, { self.min_by(Ord::cmp) } /// Returns the element that gives the maximum value from the /// specified function. /// /// If several elements are equally maximum, the last element is /// returned. If the iterator is empty, [`None`] is returned. /// /// # Examples /// /// ``` /// let a = [-3_i32, 0, 1, 5, -10]; /// assert_eq!(*a.iter().max_by_key(|x| x.abs()).unwrap(), -10); /// ``` #[inline] #[stable(feature = "iter_cmp_by_key", since = "1.6.0")] fn max_by_key(self, f: F) -> Option where Self: Sized, F: FnMut(&Self::Item) -> B, { #[inline] fn key(mut f: impl FnMut(&T) -> B) -> impl FnMut(T) -> (B, T) { move |x| (f(&x), x) } #[inline] fn compare((x_p, _): &(B, T), (y_p, _): &(B, T)) -> Ordering { x_p.cmp(y_p) } let (_, x) = self.map(key(f)).max_by(compare)?; Some(x) } /// Returns the element that gives the maximum value with respect to the /// specified comparison function. /// /// If several elements are equally maximum, the last element is /// returned. If the iterator is empty, [`None`] is returned. /// /// # Examples /// /// ``` /// let a = [-3_i32, 0, 1, 5, -10]; /// assert_eq!(*a.iter().max_by(|x, y| x.cmp(y)).unwrap(), 5); /// ``` #[inline] #[stable(feature = "iter_max_by", since = "1.15.0")] fn max_by(self, compare: F) -> Option where Self: Sized, F: FnMut(&Self::Item, &Self::Item) -> Ordering, { #[inline] fn fold(mut compare: impl FnMut(&T, &T) -> Ordering) -> impl FnMut(T, T) -> T { move |x, y| cmp::max_by(x, y, &mut compare) } self.reduce(fold(compare)) } /// Returns the element that gives the minimum value from the /// specified function. /// /// If several elements are equally minimum, the first element is /// returned. If the iterator is empty, [`None`] is returned. /// /// # Examples /// /// ``` /// let a = [-3_i32, 0, 1, 5, -10]; /// assert_eq!(*a.iter().min_by_key(|x| x.abs()).unwrap(), 0); /// ``` #[inline] #[stable(feature = "iter_cmp_by_key", since = "1.6.0")] fn min_by_key(self, f: F) -> Option where Self: Sized, F: FnMut(&Self::Item) -> B, { #[inline] fn key(mut f: impl FnMut(&T) -> B) -> impl FnMut(T) -> (B, T) { move |x| (f(&x), x) } #[inline] fn compare((x_p, _): &(B, T), (y_p, _): &(B, T)) -> Ordering { x_p.cmp(y_p) } let (_, x) = self.map(key(f)).min_by(compare)?; Some(x) } /// Returns the element that gives the minimum value with respect to the /// specified comparison function. /// /// If several elements are equally minimum, the first element is /// returned. If the iterator is empty, [`None`] is returned. /// /// # Examples /// /// ``` /// let a = [-3_i32, 0, 1, 5, -10]; /// assert_eq!(*a.iter().min_by(|x, y| x.cmp(y)).unwrap(), -10); /// ``` #[inline] #[stable(feature = "iter_min_by", since = "1.15.0")] fn min_by(self, compare: F) -> Option where Self: Sized, F: FnMut(&Self::Item, &Self::Item) -> Ordering, { #[inline] fn fold(mut compare: impl FnMut(&T, &T) -> Ordering) -> impl FnMut(T, T) -> T { move |x, y| cmp::min_by(x, y, &mut compare) } self.reduce(fold(compare)) } /// Reverses an iterator's direction. /// /// Usually, iterators iterate from left to right. After using `rev()`, /// an iterator will instead iterate from right to left. /// /// This is only possible if the iterator has an end, so `rev()` only /// works on [`DoubleEndedIterator`]s. /// /// # Examples /// /// ``` /// let a = [1, 2, 3]; /// /// let mut iter = a.iter().rev(); /// /// assert_eq!(iter.next(), Some(&3)); /// assert_eq!(iter.next(), Some(&2)); /// assert_eq!(iter.next(), Some(&1)); /// /// assert_eq!(iter.next(), None); /// ``` #[inline] #[doc(alias = "reverse")] #[stable(feature = "rust1", since = "1.0.0")] fn rev(self) -> Rev where Self: Sized + DoubleEndedIterator, { Rev::new(self) } /// Converts an iterator of pairs into a pair of containers. /// /// `unzip()` consumes an entire iterator of pairs, producing two /// collections: one from the left elements of the pairs, and one /// from the right elements. /// /// This function is, in some sense, the opposite of [`zip`]. /// /// [`zip`]: Iterator::zip /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [(1, 2), (3, 4), (5, 6)]; /// /// let (left, right): (Vec<_>, Vec<_>) = a.iter().cloned().unzip(); /// /// assert_eq!(left, [1, 3, 5]); /// assert_eq!(right, [2, 4, 6]); /// /// // you can also unzip multiple nested tuples at once /// let a = [(1, (2, 3)), (4, (5, 6))]; /// /// let (x, (y, z)): (Vec<_>, (Vec<_>, Vec<_>)) = a.iter().cloned().unzip(); /// assert_eq!(x, [1, 4]); /// assert_eq!(y, [2, 5]); /// assert_eq!(z, [3, 6]); /// ``` #[stable(feature = "rust1", since = "1.0.0")] fn unzip(self) -> (FromA, FromB) where FromA: Default + Extend, FromB: Default + Extend, Self: Sized + Iterator, { let mut unzipped: (FromA, FromB) = Default::default(); unzipped.extend(self); unzipped } /// Creates an iterator which copies all of its elements. /// /// This is useful when you have an iterator over `&T`, but you need an /// iterator over `T`. /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// /// let v_copied: Vec<_> = a.iter().copied().collect(); /// /// // copied is the same as .map(|&x| x) /// let v_map: Vec<_> = a.iter().map(|&x| x).collect(); /// /// assert_eq!(v_copied, vec![1, 2, 3]); /// assert_eq!(v_map, vec![1, 2, 3]); /// ``` #[stable(feature = "iter_copied", since = "1.36.0")] fn copied<'a, T: 'a>(self) -> Copied where Self: Sized + Iterator, T: Copy, { Copied::new(self) } /// Creates an iterator which [`clone`]s all of its elements. /// /// This is useful when you have an iterator over `&T`, but you need an /// iterator over `T`. /// /// There is no guarantee whatsoever about the `clone` method actually /// being called *or* optimized away. So code should not depend on /// either. /// /// [`clone`]: Clone::clone /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// /// let v_cloned: Vec<_> = a.iter().cloned().collect(); /// /// // cloned is the same as .map(|&x| x), for integers /// let v_map: Vec<_> = a.iter().map(|&x| x).collect(); /// /// assert_eq!(v_cloned, vec![1, 2, 3]); /// assert_eq!(v_map, vec![1, 2, 3]); /// ``` /// /// To get the best performance, try to clone late: /// /// ``` /// let a = [vec![0_u8, 1, 2], vec![3, 4], vec![23]]; /// // don't do this: /// let slower: Vec<_> = a.iter().cloned().filter(|s| s.len() == 1).collect(); /// assert_eq!(&[vec![23]], &slower[..]); /// // instead call `cloned` late /// let faster: Vec<_> = a.iter().filter(|s| s.len() == 1).cloned().collect(); /// assert_eq!(&[vec![23]], &faster[..]); /// ``` #[stable(feature = "rust1", since = "1.0.0")] fn cloned<'a, T: 'a>(self) -> Cloned where Self: Sized + Iterator, T: Clone, { Cloned::new(self) } /// Repeats an iterator endlessly. /// /// Instead of stopping at [`None`], the iterator will instead start again, /// from the beginning. After iterating again, it will start at the /// beginning again. And again. And again. Forever. Note that in case the /// original iterator is empty, the resulting iterator will also be empty. /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// /// let mut it = a.iter().cycle(); /// /// assert_eq!(it.next(), Some(&1)); /// assert_eq!(it.next(), Some(&2)); /// assert_eq!(it.next(), Some(&3)); /// assert_eq!(it.next(), Some(&1)); /// assert_eq!(it.next(), Some(&2)); /// assert_eq!(it.next(), Some(&3)); /// assert_eq!(it.next(), Some(&1)); /// ``` #[stable(feature = "rust1", since = "1.0.0")] #[inline] fn cycle(self) -> Cycle where Self: Sized + Clone, { Cycle::new(self) } /// Returns an iterator over `N` elements of the iterator at a time. /// /// The chunks do not overlap. If `N` does not divide the length of the /// iterator, then the last up to `N-1` elements will be omitted and can be /// retrieved from the [`.into_remainder()`][ArrayChunks::into_remainder] /// function of the iterator. /// /// # Panics /// /// Panics if `N` is 0. /// /// # Examples /// /// Basic usage: /// /// ``` /// #![feature(iter_array_chunks)] /// /// let mut iter = "lorem".chars().array_chunks(); /// assert_eq!(iter.next(), Some(['l', 'o'])); /// assert_eq!(iter.next(), Some(['r', 'e'])); /// assert_eq!(iter.next(), None); /// assert_eq!(iter.into_remainder().unwrap().as_slice(), &['m']); /// ``` /// /// ``` /// #![feature(iter_array_chunks)] /// /// let data = [1, 1, 2, -2, 6, 0, 3, 1]; /// // ^-----^ ^------^ /// for [x, y, z] in data.iter().array_chunks() { /// assert_eq!(x + y + z, 4); /// } /// ``` #[track_caller] #[unstable(feature = "iter_array_chunks", reason = "recently added", issue = "100450")] fn array_chunks(self) -> ArrayChunks where Self: Sized, { ArrayChunks::new(self) } /// Sums the elements of an iterator. /// /// Takes each element, adds them together, and returns the result. /// /// An empty iterator returns the zero value of the type. /// /// # Panics /// /// When calling `sum()` and a primitive integer type is being returned, this /// method will panic if the computation overflows and debug assertions are /// enabled. /// /// # Examples /// /// Basic usage: /// /// ``` /// let a = [1, 2, 3]; /// let sum: i32 = a.iter().sum(); /// /// assert_eq!(sum, 6); /// ``` #[stable(feature = "iter_arith", since = "1.11.0")] fn sum(self) -> S where Self: Sized, S: Sum, { Sum::sum(self) } /// Iterates over the entire iterator, multiplying all the elements /// /// An empty iterator returns the one value of the type. /// /// # Panics /// /// When calling `product()` and a primitive integer type is being returned, /// method will panic if the computation overflows and debug assertions are /// enabled. /// /// # Examples /// /// ``` /// fn factorial(n: u32) -> u32 { /// (1..=n).product() /// } /// assert_eq!(factorial(0), 1); /// assert_eq!(factorial(1), 1); /// assert_eq!(factorial(5), 120); /// ``` #[stable(feature = "iter_arith", since = "1.11.0")] fn product

(self) -> P where Self: Sized, P: Product, { Product::product(self) } /// [Lexicographically](Ord#lexicographical-comparison) compares the elements of this [`Iterator`] with those /// of another. /// /// # Examples /// /// ``` /// use std::cmp::Ordering; /// /// assert_eq!([1].iter().cmp([1].iter()), Ordering::Equal); /// assert_eq!([1].iter().cmp([1, 2].iter()), Ordering::Less); /// assert_eq!([1, 2].iter().cmp([1].iter()), Ordering::Greater); /// ``` #[stable(feature = "iter_order", since = "1.5.0")] fn cmp(self, other: I) -> Ordering where I: IntoIterator, Self::Item: Ord, Self: Sized, { self.cmp_by(other, |x, y| x.cmp(&y)) } /// [Lexicographically](Ord#lexicographical-comparison) compares the elements of this [`Iterator`] with those /// of another with respect to the specified comparison function. /// /// # Examples /// /// Basic usage: /// /// ``` /// #![feature(iter_order_by)] /// /// use std::cmp::Ordering; /// /// let xs = [1, 2, 3, 4]; /// let ys = [1, 4, 9, 16]; /// /// assert_eq!(xs.iter().cmp_by(&ys, |&x, &y| x.cmp(&y)), Ordering::Less); /// assert_eq!(xs.iter().cmp_by(&ys, |&x, &y| (x * x).cmp(&y)), Ordering::Equal); /// assert_eq!(xs.iter().cmp_by(&ys, |&x, &y| (2 * x).cmp(&y)), Ordering::Greater); /// ``` #[unstable(feature = "iter_order_by", issue = "64295")] fn cmp_by(mut self, other: I, mut cmp: F) -> Ordering where Self: Sized, I: IntoIterator, F: FnMut(Self::Item, I::Item) -> Ordering, { let mut other = other.into_iter(); loop { let x = match self.next() { None => { if other.next().is_none() { return Ordering::Equal; } else { return Ordering::Less; } } Some(val) => val, }; let y = match other.next() { None => return Ordering::Greater, Some(val) => val, }; match cmp(x, y) { Ordering::Equal => (), non_eq => return non_eq, } } } /// [Lexicographically](Ord#lexicographical-comparison) compares the elements of this [`Iterator`] with those /// of another. /// /// # Examples /// /// ``` /// use std::cmp::Ordering; /// /// assert_eq!([1.].iter().partial_cmp([1.].iter()), Some(Ordering::Equal)); /// assert_eq!([1.].iter().partial_cmp([1., 2.].iter()), Some(Ordering::Less)); /// assert_eq!([1., 2.].iter().partial_cmp([1.].iter()), Some(Ordering::Greater)); /// /// assert_eq!([f64::NAN].iter().partial_cmp([1.].iter()), None); /// ``` #[stable(feature = "iter_order", since = "1.5.0")] fn partial_cmp(self, other: I) -> Option where I: IntoIterator, Self::Item: PartialOrd, Self: Sized, { self.partial_cmp_by(other, |x, y| x.partial_cmp(&y)) } /// [Lexicographically](Ord#lexicographical-comparison) compares the elements of this [`Iterator`] with those /// of another with respect to the specified comparison function. /// /// # Examples /// /// Basic usage: /// /// ``` /// #![feature(iter_order_by)] /// /// use std::cmp::Ordering; /// /// let xs = [1.0, 2.0, 3.0, 4.0]; /// let ys = [1.0, 4.0, 9.0, 16.0]; /// /// assert_eq!( /// xs.iter().partial_cmp_by(&ys, |&x, &y| x.partial_cmp(&y)), /// Some(Ordering::Less) /// ); /// assert_eq!( /// xs.iter().partial_cmp_by(&ys, |&x, &y| (x * x).partial_cmp(&y)), /// Some(Ordering::Equal) /// ); /// assert_eq!( /// xs.iter().partial_cmp_by(&ys, |&x, &y| (2.0 * x).partial_cmp(&y)), /// Some(Ordering::Greater) /// ); /// ``` #[unstable(feature = "iter_order_by", issue = "64295")] fn partial_cmp_by(mut self, other: I, mut partial_cmp: F) -> Option where Self: Sized, I: IntoIterator, F: FnMut(Self::Item, I::Item) -> Option, { let mut other = other.into_iter(); loop { let x = match self.next() { None => { if other.next().is_none() { return Some(Ordering::Equal); } else { return Some(Ordering::Less); } } Some(val) => val, }; let y = match other.next() { None => return Some(Ordering::Greater), Some(val) => val, }; match partial_cmp(x, y) { Some(Ordering::Equal) => (), non_eq => return non_eq, } } } /// Determines if the elements of this [`Iterator`] are equal to those of /// another. /// /// # Examples /// /// ``` /// assert_eq!([1].iter().eq([1].iter()), true); /// assert_eq!([1].iter().eq([1, 2].iter()), false); /// ``` #[stable(feature = "iter_order", since = "1.5.0")] fn eq(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialEq, Self: Sized, { self.eq_by(other, |x, y| x == y) } /// Determines if the elements of this [`Iterator`] are equal to those of /// another with respect to the specified equality function. /// /// # Examples /// /// Basic usage: /// /// ``` /// #![feature(iter_order_by)] /// /// let xs = [1, 2, 3, 4]; /// let ys = [1, 4, 9, 16]; /// /// assert!(xs.iter().eq_by(&ys, |&x, &y| x * x == y)); /// ``` #[unstable(feature = "iter_order_by", issue = "64295")] fn eq_by(mut self, other: I, mut eq: F) -> bool where Self: Sized, I: IntoIterator, F: FnMut(Self::Item, I::Item) -> bool, { let mut other = other.into_iter(); loop { let x = match self.next() { None => return other.next().is_none(), Some(val) => val, }; let y = match other.next() { None => return false, Some(val) => val, }; if !eq(x, y) { return false; } } } /// Determines if the elements of this [`Iterator`] are unequal to those of /// another. /// /// # Examples /// /// ``` /// assert_eq!([1].iter().ne([1].iter()), false); /// assert_eq!([1].iter().ne([1, 2].iter()), true); /// ``` #[stable(feature = "iter_order", since = "1.5.0")] fn ne(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialEq, Self: Sized, { !self.eq(other) } /// Determines if the elements of this [`Iterator`] are [lexicographically](Ord#lexicographical-comparison) /// less than those of another. /// /// # Examples /// /// ``` /// assert_eq!([1].iter().lt([1].iter()), false); /// assert_eq!([1].iter().lt([1, 2].iter()), true); /// assert_eq!([1, 2].iter().lt([1].iter()), false); /// assert_eq!([1, 2].iter().lt([1, 2].iter()), false); /// ``` #[stable(feature = "iter_order", since = "1.5.0")] fn lt(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialOrd, Self: Sized, { self.partial_cmp(other) == Some(Ordering::Less) } /// Determines if the elements of this [`Iterator`] are [lexicographically](Ord#lexicographical-comparison) /// less or equal to those of another. /// /// # Examples /// /// ``` /// assert_eq!([1].iter().le([1].iter()), true); /// assert_eq!([1].iter().le([1, 2].iter()), true); /// assert_eq!([1, 2].iter().le([1].iter()), false); /// assert_eq!([1, 2].iter().le([1, 2].iter()), true); /// ``` #[stable(feature = "iter_order", since = "1.5.0")] fn le(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialOrd, Self: Sized, { matches!(self.partial_cmp(other), Some(Ordering::Less | Ordering::Equal)) } /// Determines if the elements of this [`Iterator`] are [lexicographically](Ord#lexicographical-comparison) /// greater than those of another. /// /// # Examples /// /// ``` /// assert_eq!([1].iter().gt([1].iter()), false); /// assert_eq!([1].iter().gt([1, 2].iter()), false); /// assert_eq!([1, 2].iter().gt([1].iter()), true); /// assert_eq!([1, 2].iter().gt([1, 2].iter()), false); /// ``` #[stable(feature = "iter_order", since = "1.5.0")] fn gt(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialOrd, Self: Sized, { self.partial_cmp(other) == Some(Ordering::Greater) } /// Determines if the elements of this [`Iterator`] are [lexicographically](Ord#lexicographical-comparison) /// greater than or equal to those of another. /// /// # Examples /// /// ``` /// assert_eq!([1].iter().ge([1].iter()), true); /// assert_eq!([1].iter().ge([1, 2].iter()), false); /// assert_eq!([1, 2].iter().ge([1].iter()), true); /// assert_eq!([1, 2].iter().ge([1, 2].iter()), true); /// ``` #[stable(feature = "iter_order", since = "1.5.0")] fn ge(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialOrd, Self: Sized, { matches!(self.partial_cmp(other), Some(Ordering::Greater | Ordering::Equal)) } /// Checks if the elements of this iterator are sorted. /// /// That is, for each element `a` and its following element `b`, `a <= b` must hold. If the /// iterator yields exactly zero or one element, `true` is returned. /// /// Note that if `Self::Item` is only `PartialOrd`, but not `Ord`, the above definition /// implies that this function returns `false` if any two consecutive items are not /// comparable. /// /// # Examples /// /// ``` /// #![feature(is_sorted)] /// /// assert!([1, 2, 2, 9].iter().is_sorted()); /// assert!(![1, 3, 2, 4].iter().is_sorted()); /// assert!([0].iter().is_sorted()); /// assert!(std::iter::empty::().is_sorted()); /// assert!(![0.0, 1.0, f32::NAN].iter().is_sorted()); /// ``` #[inline] #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")] fn is_sorted(self) -> bool where Self: Sized, Self::Item: PartialOrd, { self.is_sorted_by(PartialOrd::partial_cmp) } /// Checks if the elements of this iterator are sorted using the given comparator function. /// /// Instead of using `PartialOrd::partial_cmp`, this function uses the given `compare` /// function to determine the ordering of two elements. Apart from that, it's equivalent to /// [`is_sorted`]; see its documentation for more information. /// /// # Examples /// /// ``` /// #![feature(is_sorted)] /// /// assert!([1, 2, 2, 9].iter().is_sorted_by(|a, b| a.partial_cmp(b))); /// assert!(![1, 3, 2, 4].iter().is_sorted_by(|a, b| a.partial_cmp(b))); /// assert!([0].iter().is_sorted_by(|a, b| a.partial_cmp(b))); /// assert!(std::iter::empty::().is_sorted_by(|a, b| a.partial_cmp(b))); /// assert!(![0.0, 1.0, f32::NAN].iter().is_sorted_by(|a, b| a.partial_cmp(b))); /// ``` /// /// [`is_sorted`]: Iterator::is_sorted #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")] fn is_sorted_by(mut self, compare: F) -> bool where Self: Sized, F: FnMut(&Self::Item, &Self::Item) -> Option, { #[inline] fn check<'a, T>( last: &'a mut T, mut compare: impl FnMut(&T, &T) -> Option + 'a, ) -> impl FnMut(T) -> bool + 'a { move |curr| { if let Some(Ordering::Greater) | None = compare(&last, &curr) { return false; } *last = curr; true } } let mut last = match self.next() { Some(e) => e, None => return true, }; self.all(check(&mut last, compare)) } /// Checks if the elements of this iterator are sorted using the given key extraction /// function. /// /// Instead of comparing the iterator's elements directly, this function compares the keys of /// the elements, as determined by `f`. Apart from that, it's equivalent to [`is_sorted`]; see /// its documentation for more information. /// /// [`is_sorted`]: Iterator::is_sorted /// /// # Examples /// /// ``` /// #![feature(is_sorted)] /// /// assert!(["c", "bb", "aaa"].iter().is_sorted_by_key(|s| s.len())); /// assert!(![-2i32, -1, 0, 3].iter().is_sorted_by_key(|n| n.abs())); /// ``` #[inline] #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")] fn is_sorted_by_key(self, f: F) -> bool where Self: Sized, F: FnMut(Self::Item) -> K, K: PartialOrd, { self.map(f).is_sorted() } /// See [TrustedRandomAccess][super::super::TrustedRandomAccess] // The unusual name is to avoid name collisions in method resolution // see #76479. #[inline] #[doc(hidden)] #[unstable(feature = "trusted_random_access", issue = "none")] unsafe fn __iterator_get_unchecked(&mut self, _idx: usize) -> Self::Item where Self: TrustedRandomAccessNoCoerce, { unreachable!("Always specialized"); } } #[stable(feature = "rust1", since = "1.0.0")] impl Iterator for &mut I { type Item = I::Item; #[inline] fn next(&mut self) -> Option { (**self).next() } fn size_hint(&self) -> (usize, Option) { (**self).size_hint() } fn advance_by(&mut self, n: usize) -> Result<(), usize> { (**self).advance_by(n) } fn nth(&mut self, n: usize) -> Option { (**self).nth(n) } }