From 698f8c2f01ea549d77d7dc3338a12e04c11057b9 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Wed, 17 Apr 2024 14:02:58 +0200 Subject: Adding upstream version 1.64.0+dfsg1. Signed-off-by: Daniel Baumann --- library/std/src/primitive_docs.rs | 1508 +++++++++++++++++++++++++++++++++++++ 1 file changed, 1508 insertions(+) create mode 100644 library/std/src/primitive_docs.rs (limited to 'library/std/src/primitive_docs.rs') diff --git a/library/std/src/primitive_docs.rs b/library/std/src/primitive_docs.rs new file mode 100644 index 000000000..b8e546164 --- /dev/null +++ b/library/std/src/primitive_docs.rs @@ -0,0 +1,1508 @@ +// `library/{std,core}/src/primitive_docs.rs` should have the same contents. +// These are different files so that relative links work properly without +// having to have `CARGO_PKG_NAME` set, but conceptually they should always be the same. +#[doc(primitive = "bool")] +#[doc(alias = "true")] +#[doc(alias = "false")] +/// The boolean type. +/// +/// The `bool` represents a value, which could only be either [`true`] or [`false`]. If you cast +/// a `bool` into an integer, [`true`] will be 1 and [`false`] will be 0. +/// +/// # Basic usage +/// +/// `bool` implements various traits, such as [`BitAnd`], [`BitOr`], [`Not`], etc., +/// which allow us to perform boolean operations using `&`, `|` and `!`. +/// +/// [`if`] requires a `bool` value as its conditional. [`assert!`], which is an +/// important macro in testing, checks whether an expression is [`true`] and panics +/// if it isn't. +/// +/// ``` +/// let bool_val = true & false | false; +/// assert!(!bool_val); +/// ``` +/// +/// [`true`]: ../std/keyword.true.html +/// [`false`]: ../std/keyword.false.html +/// [`BitAnd`]: ops::BitAnd +/// [`BitOr`]: ops::BitOr +/// [`Not`]: ops::Not +/// [`if`]: ../std/keyword.if.html +/// +/// # Examples +/// +/// A trivial example of the usage of `bool`: +/// +/// ``` +/// let praise_the_borrow_checker = true; +/// +/// // using the `if` conditional +/// if praise_the_borrow_checker { +/// println!("oh, yeah!"); +/// } else { +/// println!("what?!!"); +/// } +/// +/// // ... or, a match pattern +/// match praise_the_borrow_checker { +/// true => println!("keep praising!"), +/// false => println!("you should praise!"), +/// } +/// ``` +/// +/// Also, since `bool` implements the [`Copy`] trait, we don't +/// have to worry about the move semantics (just like the integer and float primitives). +/// +/// Now an example of `bool` cast to integer type: +/// +/// ``` +/// assert_eq!(true as i32, 1); +/// assert_eq!(false as i32, 0); +/// ``` +#[stable(feature = "rust1", since = "1.0.0")] +mod prim_bool {} + +#[doc(primitive = "never")] +#[doc(alias = "!")] +// +/// The `!` type, also called "never". +/// +/// `!` represents the type of computations which never resolve to any value at all. For example, +/// the [`exit`] function `fn exit(code: i32) -> !` exits the process without ever returning, and +/// so returns `!`. +/// +/// `break`, `continue` and `return` expressions also have type `!`. For example we are allowed to +/// write: +/// +/// ``` +/// #![feature(never_type)] +/// # fn foo() -> u32 { +/// let x: ! = { +/// return 123 +/// }; +/// # } +/// ``` +/// +/// Although the `let` is pointless here, it illustrates the meaning of `!`. Since `x` is never +/// assigned a value (because `return` returns from the entire function), `x` can be given type +/// `!`. We could also replace `return 123` with a `panic!` or a never-ending `loop` and this code +/// would still be valid. +/// +/// A more realistic usage of `!` is in this code: +/// +/// ``` +/// # fn get_a_number() -> Option { None } +/// # loop { +/// let num: u32 = match get_a_number() { +/// Some(num) => num, +/// None => break, +/// }; +/// # } +/// ``` +/// +/// Both match arms must produce values of type [`u32`], but since `break` never produces a value +/// at all we know it can never produce a value which isn't a [`u32`]. This illustrates another +/// behaviour of the `!` type - expressions with type `!` will coerce into any other type. +/// +/// [`u32`]: prim@u32 +#[doc = concat!("[`exit`]: ", include_str!("../primitive_docs/process_exit.md"))] +/// +/// # `!` and generics +/// +/// ## Infallible errors +/// +/// The main place you'll see `!` used explicitly is in generic code. Consider the [`FromStr`] +/// trait: +/// +/// ``` +/// trait FromStr: Sized { +/// type Err; +/// fn from_str(s: &str) -> Result; +/// } +/// ``` +/// +/// When implementing this trait for [`String`] we need to pick a type for [`Err`]. And since +/// converting a string into a string will never result in an error, the appropriate type is `!`. +/// (Currently the type actually used is an enum with no variants, though this is only because `!` +/// was added to Rust at a later date and it may change in the future.) With an [`Err`] type of +/// `!`, if we have to call [`String::from_str`] for some reason the result will be a +/// [`Result`] which we can unpack like this: +/// +/// ``` +/// #![feature(exhaustive_patterns)] +/// use std::str::FromStr; +/// let Ok(s) = String::from_str("hello"); +/// ``` +/// +/// Since the [`Err`] variant contains a `!`, it can never occur. If the `exhaustive_patterns` +/// feature is present this means we can exhaustively match on [`Result`] by just taking the +/// [`Ok`] variant. This illustrates another behaviour of `!` - it can be used to "delete" certain +/// enum variants from generic types like `Result`. +/// +/// ## Infinite loops +/// +/// While [`Result`] is very useful for removing errors, `!` can also be used to remove +/// successes as well. If we think of [`Result`] as "if this function returns, it has not +/// errored," we get a very intuitive idea of [`Result`] as well: if the function returns, it +/// *has* errored. +/// +/// For example, consider the case of a simple web server, which can be simplified to: +/// +/// ```ignore (hypothetical-example) +/// loop { +/// let (client, request) = get_request().expect("disconnected"); +/// let response = request.process(); +/// response.send(client); +/// } +/// ``` +/// +/// Currently, this isn't ideal, because we simply panic whenever we fail to get a new connection. +/// Instead, we'd like to keep track of this error, like this: +/// +/// ```ignore (hypothetical-example) +/// loop { +/// match get_request() { +/// Err(err) => break err, +/// Ok((client, request)) => { +/// let response = request.process(); +/// response.send(client); +/// }, +/// } +/// } +/// ``` +/// +/// Now, when the server disconnects, we exit the loop with an error instead of panicking. While it +/// might be intuitive to simply return the error, we might want to wrap it in a [`Result`] +/// instead: +/// +/// ```ignore (hypothetical-example) +/// fn server_loop() -> Result { +/// loop { +/// let (client, request) = get_request()?; +/// let response = request.process(); +/// response.send(client); +/// } +/// } +/// ``` +/// +/// Now, we can use `?` instead of `match`, and the return type makes a lot more sense: if the loop +/// ever stops, it means that an error occurred. We don't even have to wrap the loop in an `Ok` +/// because `!` coerces to `Result` automatically. +/// +/// [`String::from_str`]: str::FromStr::from_str +#[doc = concat!("[`String`]: ", include_str!("../primitive_docs/string_string.md"))] +/// [`FromStr`]: str::FromStr +/// +/// # `!` and traits +/// +/// When writing your own traits, `!` should have an `impl` whenever there is an obvious `impl` +/// which doesn't `panic!`. The reason is that functions returning an `impl Trait` where `!` +/// does not have an `impl` of `Trait` cannot diverge as their only possible code path. In other +/// words, they can't return `!` from every code path. As an example, this code doesn't compile: +/// +/// ```compile_fail +/// use std::ops::Add; +/// +/// fn foo() -> impl Add { +/// unimplemented!() +/// } +/// ``` +/// +/// But this code does: +/// +/// ``` +/// use std::ops::Add; +/// +/// fn foo() -> impl Add { +/// if true { +/// unimplemented!() +/// } else { +/// 0 +/// } +/// } +/// ``` +/// +/// The reason is that, in the first example, there are many possible types that `!` could coerce +/// to, because many types implement `Add`. However, in the second example, +/// the `else` branch returns a `0`, which the compiler infers from the return type to be of type +/// `u32`. Since `u32` is a concrete type, `!` can and will be coerced to it. See issue [#36375] +/// for more information on this quirk of `!`. +/// +/// [#36375]: https://github.com/rust-lang/rust/issues/36375 +/// +/// As it turns out, though, most traits can have an `impl` for `!`. Take [`Debug`] +/// for example: +/// +/// ``` +/// #![feature(never_type)] +/// # use std::fmt; +/// # trait Debug { +/// # fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result; +/// # } +/// impl Debug for ! { +/// fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result { +/// *self +/// } +/// } +/// ``` +/// +/// Once again we're using `!`'s ability to coerce into any other type, in this case +/// [`fmt::Result`]. Since this method takes a `&!` as an argument we know that it can never be +/// called (because there is no value of type `!` for it to be called with). Writing `*self` +/// essentially tells the compiler "We know that this code can never be run, so just treat the +/// entire function body as having type [`fmt::Result`]". This pattern can be used a lot when +/// implementing traits for `!`. Generally, any trait which only has methods which take a `self` +/// parameter should have such an impl. +/// +/// On the other hand, one trait which would not be appropriate to implement is [`Default`]: +/// +/// ``` +/// trait Default { +/// fn default() -> Self; +/// } +/// ``` +/// +/// Since `!` has no values, it has no default value either. It's true that we could write an +/// `impl` for this which simply panics, but the same is true for any type (we could `impl +/// Default` for (eg.) [`File`] by just making [`default()`] panic.) +/// +#[doc = concat!("[`File`]: ", include_str!("../primitive_docs/fs_file.md"))] +/// [`Debug`]: fmt::Debug +/// [`default()`]: Default::default +/// +#[unstable(feature = "never_type", issue = "35121")] +mod prim_never {} + +#[doc(primitive = "char")] +#[allow(rustdoc::invalid_rust_codeblocks)] +/// A character type. +/// +/// The `char` type represents a single character. More specifically, since +/// 'character' isn't a well-defined concept in Unicode, `char` is a '[Unicode +/// scalar value]'. +/// +/// This documentation describes a number of methods and trait implementations on the +/// `char` type. For technical reasons, there is additional, separate +/// documentation in [the `std::char` module](char/index.html) as well. +/// +/// # Validity +/// +/// A `char` is a '[Unicode scalar value]', which is any '[Unicode code point]' +/// other than a [surrogate code point]. This has a fixed numerical definition: +/// code points are in the range 0 to 0x10FFFF, inclusive. +/// Surrogate code points, used by UTF-16, are in the range 0xD800 to 0xDFFF. +/// +/// No `char` may be constructed, whether as a literal or at runtime, that is not a +/// Unicode scalar value: +/// +/// ```compile_fail +/// // Each of these is a compiler error +/// ['\u{D800}', '\u{DFFF}', '\u{110000}']; +/// ``` +/// +/// ```should_panic +/// // Panics; from_u32 returns None. +/// char::from_u32(0xDE01).unwrap(); +/// ``` +/// +/// ```no_run +/// // Undefined behaviour +/// unsafe { char::from_u32_unchecked(0x110000) }; +/// ``` +/// +/// USVs are also the exact set of values that may be encoded in UTF-8. Because +/// `char` values are USVs and `str` values are valid UTF-8, it is safe to store +/// any `char` in a `str` or read any character from a `str` as a `char`. +/// +/// The gap in valid `char` values is understood by the compiler, so in the +/// below example the two ranges are understood to cover the whole range of +/// possible `char` values and there is no error for a [non-exhaustive match]. +/// +/// ``` +/// let c: char = 'a'; +/// match c { +/// '\0' ..= '\u{D7FF}' => false, +/// '\u{E000}' ..= '\u{10FFFF}' => true, +/// }; +/// ``` +/// +/// All USVs are valid `char` values, but not all of them represent a real +/// character. Many USVs are not currently assigned to a character, but may be +/// in the future ("reserved"); some will never be a character +/// ("noncharacters"); and some may be given different meanings by different +/// users ("private use"). +/// +/// [Unicode code point]: https://www.unicode.org/glossary/#code_point +/// [Unicode scalar value]: https://www.unicode.org/glossary/#unicode_scalar_value +/// [non-exhaustive match]: ../book/ch06-02-match.html#matches-are-exhaustive +/// [surrogate code point]: https://www.unicode.org/glossary/#surrogate_code_point +/// +/// # Representation +/// +/// `char` is always four bytes in size. This is a different representation than +/// a given character would have as part of a [`String`]. For example: +/// +/// ``` +/// let v = vec!['h', 'e', 'l', 'l', 'o']; +/// +/// // five elements times four bytes for each element +/// assert_eq!(20, v.len() * std::mem::size_of::()); +/// +/// let s = String::from("hello"); +/// +/// // five elements times one byte per element +/// assert_eq!(5, s.len() * std::mem::size_of::()); +/// ``` +/// +#[doc = concat!("[`String`]: ", include_str!("../primitive_docs/string_string.md"))] +/// +/// As always, remember that a human intuition for 'character' might not map to +/// Unicode's definitions. For example, despite looking similar, the 'é' +/// character is one Unicode code point while 'é' is two Unicode code points: +/// +/// ``` +/// let mut chars = "é".chars(); +/// // U+00e9: 'latin small letter e with acute' +/// assert_eq!(Some('\u{00e9}'), chars.next()); +/// assert_eq!(None, chars.next()); +/// +/// let mut chars = "é".chars(); +/// // U+0065: 'latin small letter e' +/// assert_eq!(Some('\u{0065}'), chars.next()); +/// // U+0301: 'combining acute accent' +/// assert_eq!(Some('\u{0301}'), chars.next()); +/// assert_eq!(None, chars.next()); +/// ``` +/// +/// This means that the contents of the first string above _will_ fit into a +/// `char` while the contents of the second string _will not_. Trying to create +/// a `char` literal with the contents of the second string gives an error: +/// +/// ```text +/// error: character literal may only contain one codepoint: 'é' +/// let c = 'é'; +/// ^^^ +/// ``` +/// +/// Another implication of the 4-byte fixed size of a `char` is that +/// per-`char` processing can end up using a lot more memory: +/// +/// ``` +/// let s = String::from("love: ❤️"); +/// let v: Vec = s.chars().collect(); +/// +/// assert_eq!(12, std::mem::size_of_val(&s[..])); +/// assert_eq!(32, std::mem::size_of_val(&v[..])); +/// ``` +#[stable(feature = "rust1", since = "1.0.0")] +mod prim_char {} + +#[doc(primitive = "unit")] +#[doc(alias = "(")] +#[doc(alias = ")")] +#[doc(alias = "()")] +// +/// The `()` type, also called "unit". +/// +/// The `()` type has exactly one value `()`, and is used when there +/// is no other meaningful value that could be returned. `()` is most +/// commonly seen implicitly: functions without a `-> ...` implicitly +/// have return type `()`, that is, these are equivalent: +/// +/// ```rust +/// fn long() -> () {} +/// +/// fn short() {} +/// ``` +/// +/// The semicolon `;` can be used to discard the result of an +/// expression at the end of a block, making the expression (and thus +/// the block) evaluate to `()`. For example, +/// +/// ```rust +/// fn returns_i64() -> i64 { +/// 1i64 +/// } +/// fn returns_unit() { +/// 1i64; +/// } +/// +/// let is_i64 = { +/// returns_i64() +/// }; +/// let is_unit = { +/// returns_i64(); +/// }; +/// ``` +/// +#[stable(feature = "rust1", since = "1.0.0")] +mod prim_unit {} + +// Required to make auto trait impls render. +// See src/librustdoc/passes/collect_trait_impls.rs:collect_trait_impls +#[doc(hidden)] +impl () {} + +// Fake impl that's only really used for docs. +#[cfg(doc)] +#[stable(feature = "rust1", since = "1.0.0")] +impl Clone for () { + fn clone(&self) -> Self { + loop {} + } +} + +// Fake impl that's only really used for docs. +#[cfg(doc)] +#[stable(feature = "rust1", since = "1.0.0")] +impl Copy for () { + // empty +} + +#[doc(primitive = "pointer")] +#[doc(alias = "ptr")] +#[doc(alias = "*")] +#[doc(alias = "*const")] +#[doc(alias = "*mut")] +// +/// Raw, unsafe pointers, `*const T`, and `*mut T`. +/// +/// *[See also the `std::ptr` module](ptr).* +/// +/// Working with raw pointers in Rust is uncommon, typically limited to a few patterns. +/// Raw pointers can be unaligned or [`null`]. However, when a raw pointer is +/// dereferenced (using the `*` operator), it must be non-null and aligned. +/// +/// Storing through a raw pointer using `*ptr = data` calls `drop` on the old value, so +/// [`write`] must be used if the type has drop glue and memory is not already +/// initialized - otherwise `drop` would be called on the uninitialized memory. +/// +/// Use the [`null`] and [`null_mut`] functions to create null pointers, and the +/// [`is_null`] method of the `*const T` and `*mut T` types to check for null. +/// The `*const T` and `*mut T` types also define the [`offset`] method, for +/// pointer math. +/// +/// # Common ways to create raw pointers +/// +/// ## 1. Coerce a reference (`&T`) or mutable reference (`&mut T`). +/// +/// ``` +/// let my_num: i32 = 10; +/// let my_num_ptr: *const i32 = &my_num; +/// let mut my_speed: i32 = 88; +/// let my_speed_ptr: *mut i32 = &mut my_speed; +/// ``` +/// +/// To get a pointer to a boxed value, dereference the box: +/// +/// ``` +/// let my_num: Box = Box::new(10); +/// let my_num_ptr: *const i32 = &*my_num; +/// let mut my_speed: Box = Box::new(88); +/// let my_speed_ptr: *mut i32 = &mut *my_speed; +/// ``` +/// +/// This does not take ownership of the original allocation +/// and requires no resource management later, +/// but you must not use the pointer after its lifetime. +/// +/// ## 2. Consume a box (`Box`). +/// +/// The [`into_raw`] function consumes a box and returns +/// the raw pointer. It doesn't destroy `T` or deallocate any memory. +/// +/// ``` +/// let my_speed: Box = Box::new(88); +/// let my_speed: *mut i32 = Box::into_raw(my_speed); +/// +/// // By taking ownership of the original `Box` though +/// // we are obligated to put it together later to be destroyed. +/// unsafe { +/// drop(Box::from_raw(my_speed)); +/// } +/// ``` +/// +/// Note that here the call to [`drop`] is for clarity - it indicates +/// that we are done with the given value and it should be destroyed. +/// +/// ## 3. Create it using `ptr::addr_of!` +/// +/// Instead of coercing a reference to a raw pointer, you can use the macros +/// [`ptr::addr_of!`] (for `*const T`) and [`ptr::addr_of_mut!`] (for `*mut T`). +/// These macros allow you to create raw pointers to fields to which you cannot +/// create a reference (without causing undefined behaviour), such as an +/// unaligned field. This might be necessary if packed structs or uninitialized +/// memory is involved. +/// +/// ``` +/// #[derive(Debug, Default, Copy, Clone)] +/// #[repr(C, packed)] +/// struct S { +/// aligned: u8, +/// unaligned: u32, +/// } +/// let s = S::default(); +/// let p = std::ptr::addr_of!(s.unaligned); // not allowed with coercion +/// ``` +/// +/// ## 4. Get it from C. +/// +/// ``` +/// # #![feature(rustc_private)] +/// extern crate libc; +/// +/// use std::mem; +/// +/// unsafe { +/// let my_num: *mut i32 = libc::malloc(mem::size_of::()) as *mut i32; +/// if my_num.is_null() { +/// panic!("failed to allocate memory"); +/// } +/// libc::free(my_num as *mut libc::c_void); +/// } +/// ``` +/// +/// Usually you wouldn't literally use `malloc` and `free` from Rust, +/// but C APIs hand out a lot of pointers generally, so are a common source +/// of raw pointers in Rust. +/// +/// [`null`]: ptr::null +/// [`null_mut`]: ptr::null_mut +/// [`is_null`]: pointer::is_null +/// [`offset`]: pointer::offset +#[doc = concat!("[`into_raw`]: ", include_str!("../primitive_docs/box_into_raw.md"))] +/// [`drop`]: mem::drop +/// [`write`]: ptr::write +#[stable(feature = "rust1", since = "1.0.0")] +mod prim_pointer {} + +#[doc(primitive = "array")] +#[doc(alias = "[]")] +#[doc(alias = "[T;N]")] // unfortunately, rustdoc doesn't have fuzzy search for aliases +#[doc(alias = "[T; N]")] +/// A fixed-size array, denoted `[T; N]`, for the element type, `T`, and the +/// non-negative compile-time constant size, `N`. +/// +/// There are two syntactic forms for creating an array: +/// +/// * A list with each element, i.e., `[x, y, z]`. +/// * A repeat expression `[x; N]`, which produces an array with `N` copies of `x`. +/// The type of `x` must be [`Copy`]. +/// +/// Note that `[expr; 0]` is allowed, and produces an empty array. +/// This will still evaluate `expr`, however, and immediately drop the resulting value, so +/// be mindful of side effects. +/// +/// Arrays of *any* size implement the following traits if the element type allows it: +/// +/// - [`Copy`] +/// - [`Clone`] +/// - [`Debug`] +/// - [`IntoIterator`] (implemented for `[T; N]`, `&[T; N]` and `&mut [T; N]`) +/// - [`PartialEq`], [`PartialOrd`], [`Eq`], [`Ord`] +/// - [`Hash`] +/// - [`AsRef`], [`AsMut`] +/// - [`Borrow`], [`BorrowMut`] +/// +/// Arrays of sizes from 0 to 32 (inclusive) implement the [`Default`] trait +/// if the element type allows it. As a stopgap, trait implementations are +/// statically generated up to size 32. +/// +/// Arrays coerce to [slices (`[T]`)][slice], so a slice method may be called on +/// an array. Indeed, this provides most of the API for working with arrays. +/// Slices have a dynamic size and do not coerce to arrays. +/// +/// You can move elements out of an array with a [slice pattern]. If you want +/// one element, see [`mem::replace`]. +/// +/// # Examples +/// +/// ``` +/// let mut array: [i32; 3] = [0; 3]; +/// +/// array[1] = 1; +/// array[2] = 2; +/// +/// assert_eq!([1, 2], &array[1..]); +/// +/// // This loop prints: 0 1 2 +/// for x in array { +/// print!("{x} "); +/// } +/// ``` +/// +/// You can also iterate over reference to the array's elements: +/// +/// ``` +/// let array: [i32; 3] = [0; 3]; +/// +/// for x in &array { } +/// ``` +/// +/// You can use a [slice pattern] to move elements out of an array: +/// +/// ``` +/// fn move_away(_: String) { /* Do interesting things. */ } +/// +/// let [john, roa] = ["John".to_string(), "Roa".to_string()]; +/// move_away(john); +/// move_away(roa); +/// ``` +/// +/// # Editions +/// +/// Prior to Rust 1.53, arrays did not implement [`IntoIterator`] by value, so the method call +/// `array.into_iter()` auto-referenced into a [slice iterator](slice::iter). Right now, the old +/// behavior is preserved in the 2015 and 2018 editions of Rust for compatibility, ignoring +/// [`IntoIterator`] by value. In the future, the behavior on the 2015 and 2018 edition +/// might be made consistent to the behavior of later editions. +/// +/// ```rust,edition2018 +/// // Rust 2015 and 2018: +/// +/// # #![allow(array_into_iter)] // override our `deny(warnings)` +/// let array: [i32; 3] = [0; 3]; +/// +/// // This creates a slice iterator, producing references to each value. +/// for item in array.into_iter().enumerate() { +/// let (i, x): (usize, &i32) = item; +/// println!("array[{i}] = {x}"); +/// } +/// +/// // The `array_into_iter` lint suggests this change for future compatibility: +/// for item in array.iter().enumerate() { +/// let (i, x): (usize, &i32) = item; +/// println!("array[{i}] = {x}"); +/// } +/// +/// // You can explicitly iterate an array by value using `IntoIterator::into_iter` +/// for item in IntoIterator::into_iter(array).enumerate() { +/// let (i, x): (usize, i32) = item; +/// println!("array[{i}] = {x}"); +/// } +/// ``` +/// +/// Starting in the 2021 edition, `array.into_iter()` uses `IntoIterator` normally to iterate +/// by value, and `iter()` should be used to iterate by reference like previous editions. +/// +/// ```rust,edition2021 +/// // Rust 2021: +/// +/// let array: [i32; 3] = [0; 3]; +/// +/// // This iterates by reference: +/// for item in array.iter().enumerate() { +/// let (i, x): (usize, &i32) = item; +/// println!("array[{i}] = {x}"); +/// } +/// +/// // This iterates by value: +/// for item in array.into_iter().enumerate() { +/// let (i, x): (usize, i32) = item; +/// println!("array[{i}] = {x}"); +/// } +/// ``` +/// +/// Future language versions might start treating the `array.into_iter()` +/// syntax on editions 2015 and 2018 the same as on edition 2021. So code using +/// those older editions should still be written with this change in mind, to +/// prevent breakage in the future. The safest way to accomplish this is to +/// avoid the `into_iter` syntax on those editions. If an edition update is not +/// viable/desired, there are multiple alternatives: +/// * use `iter`, equivalent to the old behavior, creating references +/// * use [`IntoIterator::into_iter`], equivalent to the post-2021 behavior (Rust 1.53+) +/// * replace `for ... in array.into_iter() {` with `for ... in array {`, +/// equivalent to the post-2021 behavior (Rust 1.53+) +/// +/// ```rust,edition2018 +/// // Rust 2015 and 2018: +/// +/// let array: [i32; 3] = [0; 3]; +/// +/// // This iterates by reference: +/// for item in array.iter() { +/// let x: &i32 = item; +/// println!("{x}"); +/// } +/// +/// // This iterates by value: +/// for item in IntoIterator::into_iter(array) { +/// let x: i32 = item; +/// println!("{x}"); +/// } +/// +/// // This iterates by value: +/// for item in array { +/// let x: i32 = item; +/// println!("{x}"); +/// } +/// +/// // IntoIter can also start a chain. +/// // This iterates by value: +/// for item in IntoIterator::into_iter(array).enumerate() { +/// let (i, x): (usize, i32) = item; +/// println!("array[{i}] = {x}"); +/// } +/// ``` +/// +/// [slice]: prim@slice +/// [`Debug`]: fmt::Debug +/// [`Hash`]: hash::Hash +/// [`Borrow`]: borrow::Borrow +/// [`BorrowMut`]: borrow::BorrowMut +/// [slice pattern]: ../reference/patterns.html#slice-patterns +#[stable(feature = "rust1", since = "1.0.0")] +mod prim_array {} + +#[doc(primitive = "slice")] +#[doc(alias = "[")] +#[doc(alias = "]")] +#[doc(alias = "[]")] +/// A dynamically-sized view into a contiguous sequence, `[T]`. Contiguous here +/// means that elements are laid out so that every element is the same +/// distance from its neighbors. +/// +/// *[See also the `std::slice` module](crate::slice).* +/// +/// Slices are a view into a block of memory represented as a pointer and a +/// length. +/// +/// ``` +/// // slicing a Vec +/// let vec = vec![1, 2, 3]; +/// let int_slice = &vec[..]; +/// // coercing an array to a slice +/// let str_slice: &[&str] = &["one", "two", "three"]; +/// ``` +/// +/// Slices are either mutable or shared. The shared slice type is `&[T]`, +/// while the mutable slice type is `&mut [T]`, where `T` represents the element +/// type. For example, you can mutate the block of memory that a mutable slice +/// points to: +/// +/// ``` +/// let mut x = [1, 2, 3]; +/// let x = &mut x[..]; // Take a full slice of `x`. +/// x[1] = 7; +/// assert_eq!(x, &[1, 7, 3]); +/// ``` +/// +/// As slices store the length of the sequence they refer to, they have twice +/// the size of pointers to [`Sized`](marker/trait.Sized.html) types. +/// Also see the reference on +/// [dynamically sized types](../reference/dynamically-sized-types.html). +/// +/// ``` +/// # use std::rc::Rc; +/// let pointer_size = std::mem::size_of::<&u8>(); +/// assert_eq!(2 * pointer_size, std::mem::size_of::<&[u8]>()); +/// assert_eq!(2 * pointer_size, std::mem::size_of::<*const [u8]>()); +/// assert_eq!(2 * pointer_size, std::mem::size_of::>()); +/// assert_eq!(2 * pointer_size, std::mem::size_of::>()); +/// ``` +#[stable(feature = "rust1", since = "1.0.0")] +mod prim_slice {} + +#[doc(primitive = "str")] +// +/// String slices. +/// +/// *[See also the `std::str` module](crate::str).* +/// +/// The `str` type, also called a 'string slice', is the most primitive string +/// type. It is usually seen in its borrowed form, `&str`. It is also the type +/// of string literals, `&'static str`. +/// +/// String slices are always valid UTF-8. +/// +/// # Examples +/// +/// String literals are string slices: +/// +/// ``` +/// let hello = "Hello, world!"; +/// +/// // with an explicit type annotation +/// let hello: &'static str = "Hello, world!"; +/// ``` +/// +/// They are `'static` because they're stored directly in the final binary, and +/// so will be valid for the `'static` duration. +/// +/// # Representation +/// +/// A `&str` is made up of two components: a pointer to some bytes, and a +/// length. You can look at these with the [`as_ptr`] and [`len`] methods: +/// +/// ``` +/// use std::slice; +/// use std::str; +/// +/// let story = "Once upon a time..."; +/// +/// let ptr = story.as_ptr(); +/// let len = story.len(); +/// +/// // story has nineteen bytes +/// assert_eq!(19, len); +/// +/// // We can re-build a str out of ptr and len. This is all unsafe because +/// // we are responsible for making sure the two components are valid: +/// let s = unsafe { +/// // First, we build a &[u8]... +/// let slice = slice::from_raw_parts(ptr, len); +/// +/// // ... and then convert that slice into a string slice +/// str::from_utf8(slice) +/// }; +/// +/// assert_eq!(s, Ok(story)); +/// ``` +/// +/// [`as_ptr`]: str::as_ptr +/// [`len`]: str::len +/// +/// Note: This example shows the internals of `&str`. `unsafe` should not be +/// used to get a string slice under normal circumstances. Use `as_str` +/// instead. +#[stable(feature = "rust1", since = "1.0.0")] +mod prim_str {} + +#[doc(primitive = "tuple")] +#[doc(alias = "(")] +#[doc(alias = ")")] +#[doc(alias = "()")] +// +/// A finite heterogeneous sequence, `(T, U, ..)`. +/// +/// Let's cover each of those in turn: +/// +/// Tuples are *finite*. In other words, a tuple has a length. Here's a tuple +/// of length `3`: +/// +/// ``` +/// ("hello", 5, 'c'); +/// ``` +/// +/// 'Length' is also sometimes called 'arity' here; each tuple of a different +/// length is a different, distinct type. +/// +/// Tuples are *heterogeneous*. This means that each element of the tuple can +/// have a different type. In that tuple above, it has the type: +/// +/// ``` +/// # let _: +/// (&'static str, i32, char) +/// # = ("hello", 5, 'c'); +/// ``` +/// +/// Tuples are a *sequence*. This means that they can be accessed by position; +/// this is called 'tuple indexing', and it looks like this: +/// +/// ```rust +/// let tuple = ("hello", 5, 'c'); +/// +/// assert_eq!(tuple.0, "hello"); +/// assert_eq!(tuple.1, 5); +/// assert_eq!(tuple.2, 'c'); +/// ``` +/// +/// The sequential nature of the tuple applies to its implementations of various +/// traits. For example, in [`PartialOrd`] and [`Ord`], the elements are compared +/// sequentially until the first non-equal set is found. +/// +/// For more about tuples, see [the book](../book/ch03-02-data-types.html#the-tuple-type). +/// +// Hardcoded anchor in src/librustdoc/html/format.rs +// linked to as `#trait-implementations-1` +/// # Trait implementations +/// +/// In this documentation the shorthand `(T₁, T₂, …, Tₙ)` is used to represent tuples of varying +/// length. When that is used, any trait bound expressed on `T` applies to each element of the +/// tuple independently. Note that this is a convenience notation to avoid repetitive +/// documentation, not valid Rust syntax. +/// +/// Due to a temporary restriction in Rust’s type system, the following traits are only +/// implemented on tuples of arity 12 or less. In the future, this may change: +/// +/// * [`PartialEq`] +/// * [`Eq`] +/// * [`PartialOrd`] +/// * [`Ord`] +/// * [`Debug`] +/// * [`Default`] +/// * [`Hash`] +/// +/// [`Debug`]: fmt::Debug +/// [`Hash`]: hash::Hash +/// +/// The following traits are implemented for tuples of any length. These traits have +/// implementations that are automatically generated by the compiler, so are not limited by +/// missing language features. +/// +/// * [`Clone`] +/// * [`Copy`] +/// * [`Send`] +/// * [`Sync`] +/// * [`Unpin`] +/// * [`UnwindSafe`] +/// * [`RefUnwindSafe`] +/// +/// [`Unpin`]: marker::Unpin +/// [`UnwindSafe`]: panic::UnwindSafe +/// [`RefUnwindSafe`]: panic::RefUnwindSafe +/// +/// # Examples +/// +/// Basic usage: +/// +/// ``` +/// let tuple = ("hello", 5, 'c'); +/// +/// assert_eq!(tuple.0, "hello"); +/// ``` +/// +/// Tuples are often used as a return type when you want to return more than +/// one value: +/// +/// ``` +/// fn calculate_point() -> (i32, i32) { +/// // Don't do a calculation, that's not the point of the example +/// (4, 5) +/// } +/// +/// let point = calculate_point(); +/// +/// assert_eq!(point.0, 4); +/// assert_eq!(point.1, 5); +/// +/// // Combining this with patterns can be nicer. +/// +/// let (x, y) = calculate_point(); +/// +/// assert_eq!(x, 4); +/// assert_eq!(y, 5); +/// ``` +/// +#[stable(feature = "rust1", since = "1.0.0")] +mod prim_tuple {} + +// Required to make auto trait impls render. +// See src/librustdoc/passes/collect_trait_impls.rs:collect_trait_impls +#[doc(hidden)] +impl (T,) {} + +// Fake impl that's only really used for docs. +#[cfg(doc)] +#[stable(feature = "rust1", since = "1.0.0")] +#[cfg_attr(not(bootstrap), doc(fake_variadic))] +/// This trait is implemented on arbitrary-length tuples. +impl Clone for (T,) { + fn clone(&self) -> Self { + loop {} + } +} + +// Fake impl that's only really used for docs. +#[cfg(doc)] +#[stable(feature = "rust1", since = "1.0.0")] +#[cfg_attr(not(bootstrap), doc(fake_variadic))] +/// This trait is implemented on arbitrary-length tuples. +impl Copy for (T,) { + // empty +} + +#[doc(primitive = "f32")] +/// A 32-bit floating point type (specifically, the "binary32" type defined in IEEE 754-2008). +/// +/// This type can represent a wide range of decimal numbers, like `3.5`, `27`, +/// `-113.75`, `0.0078125`, `34359738368`, `0`, `-1`. So unlike integer types +/// (such as `i32`), floating point types can represent non-integer numbers, +/// too. +/// +/// However, being able to represent this wide range of numbers comes at the +/// cost of precision: floats can only represent some of the real numbers and +/// calculation with floats round to a nearby representable number. For example, +/// `5.0` and `1.0` can be exactly represented as `f32`, but `1.0 / 5.0` results +/// in `0.20000000298023223876953125` since `0.2` cannot be exactly represented +/// as `f32`. Note, however, that printing floats with `println` and friends will +/// often discard insignificant digits: `println!("{}", 1.0f32 / 5.0f32)` will +/// print `0.2`. +/// +/// Additionally, `f32` can represent some special values: +/// +/// - −0.0: IEEE 754 floating point numbers have a bit that indicates their sign, so −0.0 is a +/// possible value. For comparison −0.0 = +0.0, but floating point operations can carry +/// the sign bit through arithmetic operations. This means −0.0 × +0.0 produces −0.0 and +/// a negative number rounded to a value smaller than a float can represent also produces −0.0. +/// - [∞](#associatedconstant.INFINITY) and +/// [−∞](#associatedconstant.NEG_INFINITY): these result from calculations +/// like `1.0 / 0.0`. +/// - [NaN (not a number)](#associatedconstant.NAN): this value results from +/// calculations like `(-1.0).sqrt()`. NaN has some potentially unexpected +/// behavior: +/// - It is unequal to any float, including itself! This is the reason `f32` +/// doesn't implement the `Eq` trait. +/// - It is also neither smaller nor greater than any float, making it +/// impossible to sort by the default comparison operation, which is the +/// reason `f32` doesn't implement the `Ord` trait. +/// - It is also considered *infectious* as almost all calculations where one +/// of the operands is NaN will also result in NaN. The explanations on this +/// page only explicitly document behavior on NaN operands if this default +/// is deviated from. +/// - Lastly, there are multiple bit patterns that are considered NaN. +/// Rust does not currently guarantee that the bit patterns of NaN are +/// preserved over arithmetic operations, and they are not guaranteed to be +/// portable or even fully deterministic! This means that there may be some +/// surprising results upon inspecting the bit patterns, +/// as the same calculations might produce NaNs with different bit patterns. +/// +/// When the number resulting from a primitive operation (addition, +/// subtraction, multiplication, or division) on this type is not exactly +/// representable as `f32`, it is rounded according to the roundTiesToEven +/// direction defined in IEEE 754-2008. That means: +/// +/// - The result is the representable value closest to the true value, if there +/// is a unique closest representable value. +/// - If the true value is exactly half-way between two representable values, +/// the result is the one with an even least-significant binary digit. +/// - If the true value's magnitude is ≥ `f32::MAX` + 2(`f32::MAX_EXP` − +/// `f32::MANTISSA_DIGITS` − 1), the result is ∞ or −∞ (preserving the +/// true value's sign). +/// +/// For more information on floating point numbers, see [Wikipedia][wikipedia]. +/// +/// *[See also the `std::f32::consts` module](crate::f32::consts).* +/// +/// [wikipedia]: https://en.wikipedia.org/wiki/Single-precision_floating-point_format +#[stable(feature = "rust1", since = "1.0.0")] +mod prim_f32 {} + +#[doc(primitive = "f64")] +/// A 64-bit floating point type (specifically, the "binary64" type defined in IEEE 754-2008). +/// +/// This type is very similar to [`f32`], but has increased +/// precision by using twice as many bits. Please see [the documentation for +/// `f32`][`f32`] or [Wikipedia on double precision +/// values][wikipedia] for more information. +/// +/// *[See also the `std::f64::consts` module](crate::f64::consts).* +/// +/// [`f32`]: prim@f32 +/// [wikipedia]: https://en.wikipedia.org/wiki/Double-precision_floating-point_format +#[stable(feature = "rust1", since = "1.0.0")] +mod prim_f64 {} + +#[doc(primitive = "i8")] +// +/// The 8-bit signed integer type. +#[stable(feature = "rust1", since = "1.0.0")] +mod prim_i8 {} + +#[doc(primitive = "i16")] +// +/// The 16-bit signed integer type. +#[stable(feature = "rust1", since = "1.0.0")] +mod prim_i16 {} + +#[doc(primitive = "i32")] +// +/// The 32-bit signed integer type. +#[stable(feature = "rust1", since = "1.0.0")] +mod prim_i32 {} + +#[doc(primitive = "i64")] +// +/// The 64-bit signed integer type. +#[stable(feature = "rust1", since = "1.0.0")] +mod prim_i64 {} + +#[doc(primitive = "i128")] +// +/// The 128-bit signed integer type. +#[stable(feature = "i128", since = "1.26.0")] +mod prim_i128 {} + +#[doc(primitive = "u8")] +// +/// The 8-bit unsigned integer type. +#[stable(feature = "rust1", since = "1.0.0")] +mod prim_u8 {} + +#[doc(primitive = "u16")] +// +/// The 16-bit unsigned integer type. +#[stable(feature = "rust1", since = "1.0.0")] +mod prim_u16 {} + +#[doc(primitive = "u32")] +// +/// The 32-bit unsigned integer type. +#[stable(feature = "rust1", since = "1.0.0")] +mod prim_u32 {} + +#[doc(primitive = "u64")] +// +/// The 64-bit unsigned integer type. +#[stable(feature = "rust1", since = "1.0.0")] +mod prim_u64 {} + +#[doc(primitive = "u128")] +// +/// The 128-bit unsigned integer type. +#[stable(feature = "i128", since = "1.26.0")] +mod prim_u128 {} + +#[doc(primitive = "isize")] +// +/// The pointer-sized signed integer type. +/// +/// The size of this primitive is how many bytes it takes to reference any +/// location in memory. For example, on a 32 bit target, this is 4 bytes +/// and on a 64 bit target, this is 8 bytes. +#[stable(feature = "rust1", since = "1.0.0")] +mod prim_isize {} + +#[doc(primitive = "usize")] +// +/// The pointer-sized unsigned integer type. +/// +/// The size of this primitive is how many bytes it takes to reference any +/// location in memory. For example, on a 32 bit target, this is 4 bytes +/// and on a 64 bit target, this is 8 bytes. +#[stable(feature = "rust1", since = "1.0.0")] +mod prim_usize {} + +#[doc(primitive = "reference")] +#[doc(alias = "&")] +#[doc(alias = "&mut")] +// +/// References, both shared and mutable. +/// +/// A reference represents a borrow of some owned value. You can get one by using the `&` or `&mut` +/// operators on a value, or by using a [`ref`](../std/keyword.ref.html) or +/// [ref](../std/keyword.ref.html) [mut](../std/keyword.mut.html) pattern. +/// +/// For those familiar with pointers, a reference is just a pointer that is assumed to be +/// aligned, not null, and pointing to memory containing a valid value of `T` - for example, +/// &[bool] can only point to an allocation containing the integer values `1` +/// ([`true`](../std/keyword.true.html)) or `0` ([`false`](../std/keyword.false.html)), but +/// creating a &[bool] that points to an allocation containing +/// the value `3` causes undefined behaviour. +/// In fact, [Option]\<&T> has the same memory representation as a +/// nullable but aligned pointer, and can be passed across FFI boundaries as such. +/// +/// In most cases, references can be used much like the original value. Field access, method +/// calling, and indexing work the same (save for mutability rules, of course). In addition, the +/// comparison operators transparently defer to the referent's implementation, allowing references +/// to be compared the same as owned values. +/// +/// References have a lifetime attached to them, which represents the scope for which the borrow is +/// valid. A lifetime is said to "outlive" another one if its representative scope is as long or +/// longer than the other. The `'static` lifetime is the longest lifetime, which represents the +/// total life of the program. For example, string literals have a `'static` lifetime because the +/// text data is embedded into the binary of the program, rather than in an allocation that needs +/// to be dynamically managed. +/// +/// `&mut T` references can be freely coerced into `&T` references with the same referent type, and +/// references with longer lifetimes can be freely coerced into references with shorter ones. +/// +/// Reference equality by address, instead of comparing the values pointed to, is accomplished via +/// implicit reference-pointer coercion and raw pointer equality via [`ptr::eq`], while +/// [`PartialEq`] compares values. +/// +/// ``` +/// use std::ptr; +/// +/// let five = 5; +/// let other_five = 5; +/// let five_ref = &five; +/// let same_five_ref = &five; +/// let other_five_ref = &other_five; +/// +/// assert!(five_ref == same_five_ref); +/// assert!(five_ref == other_five_ref); +/// +/// assert!(ptr::eq(five_ref, same_five_ref)); +/// assert!(!ptr::eq(five_ref, other_five_ref)); +/// ``` +/// +/// For more information on how to use references, see [the book's section on "References and +/// Borrowing"][book-refs]. +/// +/// [book-refs]: ../book/ch04-02-references-and-borrowing.html +/// +/// # Trait implementations +/// +/// The following traits are implemented for all `&T`, regardless of the type of its referent: +/// +/// * [`Copy`] +/// * [`Clone`] \(Note that this will not defer to `T`'s `Clone` implementation if it exists!) +/// * [`Deref`] +/// * [`Borrow`] +/// * [`fmt::Pointer`] +/// +/// [`Deref`]: ops::Deref +/// [`Borrow`]: borrow::Borrow +/// +/// `&mut T` references get all of the above except `Copy` and `Clone` (to prevent creating +/// multiple simultaneous mutable borrows), plus the following, regardless of the type of its +/// referent: +/// +/// * [`DerefMut`] +/// * [`BorrowMut`] +/// +/// [`DerefMut`]: ops::DerefMut +/// [`BorrowMut`]: borrow::BorrowMut +/// [bool]: prim@bool +/// +/// The following traits are implemented on `&T` references if the underlying `T` also implements +/// that trait: +/// +/// * All the traits in [`std::fmt`] except [`fmt::Pointer`] (which is implemented regardless of the type of its referent) and [`fmt::Write`] +/// * [`PartialOrd`] +/// * [`Ord`] +/// * [`PartialEq`] +/// * [`Eq`] +/// * [`AsRef`] +/// * [`Fn`] \(in addition, `&T` references get [`FnMut`] and [`FnOnce`] if `T: Fn`) +/// * [`Hash`] +/// * [`ToSocketAddrs`] +/// * [`Send`] \(`&T` references also require T: [Sync]) +/// +/// [`std::fmt`]: fmt +/// [`Hash`]: hash::Hash +#[doc = concat!("[`ToSocketAddrs`]: ", include_str!("../primitive_docs/net_tosocketaddrs.md"))] +/// +/// `&mut T` references get all of the above except `ToSocketAddrs`, plus the following, if `T` +/// implements that trait: +/// +/// * [`AsMut`] +/// * [`FnMut`] \(in addition, `&mut T` references get [`FnOnce`] if `T: FnMut`) +/// * [`fmt::Write`] +/// * [`Iterator`] +/// * [`DoubleEndedIterator`] +/// * [`ExactSizeIterator`] +/// * [`FusedIterator`] +/// * [`TrustedLen`] +/// * [`io::Write`] +/// * [`Read`] +/// * [`Seek`] +/// * [`BufRead`] +/// +/// [`FusedIterator`]: iter::FusedIterator +/// [`TrustedLen`]: iter::TrustedLen +#[doc = concat!("[`Seek`]: ", include_str!("../primitive_docs/io_seek.md"))] +#[doc = concat!("[`BufRead`]: ", include_str!("../primitive_docs/io_bufread.md"))] +#[doc = concat!("[`Read`]: ", include_str!("../primitive_docs/io_read.md"))] +#[doc = concat!("[`io::Write`]: ", include_str!("../primitive_docs/io_write.md"))] +/// +/// Note that due to method call deref coercion, simply calling a trait method will act like they +/// work on references as well as they do on owned values! The implementations described here are +/// meant for generic contexts, where the final type `T` is a type parameter or otherwise not +/// locally known. +#[stable(feature = "rust1", since = "1.0.0")] +mod prim_ref {} + +#[doc(primitive = "fn")] +// +/// Function pointers, like `fn(usize) -> bool`. +/// +/// *See also the traits [`Fn`], [`FnMut`], and [`FnOnce`].* +/// +/// [`Fn`]: ops::Fn +/// [`FnMut`]: ops::FnMut +/// [`FnOnce`]: ops::FnOnce +/// +/// Function pointers are pointers that point to *code*, not data. They can be called +/// just like functions. Like references, function pointers are, among other things, assumed to +/// not be null, so if you want to pass a function pointer over FFI and be able to accommodate null +/// pointers, make your type [`Option`](core::option#options-and-pointers-nullable-pointers) +/// with your required signature. +/// +/// ### Safety +/// +/// Plain function pointers are obtained by casting either plain functions, or closures that don't +/// capture an environment: +/// +/// ``` +/// fn add_one(x: usize) -> usize { +/// x + 1 +/// } +/// +/// let ptr: fn(usize) -> usize = add_one; +/// assert_eq!(ptr(5), 6); +/// +/// let clos: fn(usize) -> usize = |x| x + 5; +/// assert_eq!(clos(5), 10); +/// ``` +/// +/// In addition to varying based on their signature, function pointers come in two flavors: safe +/// and unsafe. Plain `fn()` function pointers can only point to safe functions, +/// while `unsafe fn()` function pointers can point to safe or unsafe functions. +/// +/// ``` +/// fn add_one(x: usize) -> usize { +/// x + 1 +/// } +/// +/// unsafe fn add_one_unsafely(x: usize) -> usize { +/// x + 1 +/// } +/// +/// let safe_ptr: fn(usize) -> usize = add_one; +/// +/// //ERROR: mismatched types: expected normal fn, found unsafe fn +/// //let bad_ptr: fn(usize) -> usize = add_one_unsafely; +/// +/// let unsafe_ptr: unsafe fn(usize) -> usize = add_one_unsafely; +/// let really_safe_ptr: unsafe fn(usize) -> usize = add_one; +/// ``` +/// +/// ### ABI +/// +/// On top of that, function pointers can vary based on what ABI they use. This +/// is achieved by adding the `extern` keyword before the type, followed by the +/// ABI in question. The default ABI is "Rust", i.e., `fn()` is the exact same +/// type as `extern "Rust" fn()`. A pointer to a function with C ABI would have +/// type `extern "C" fn()`. +/// +/// `extern "ABI" { ... }` blocks declare functions with ABI "ABI". The default +/// here is "C", i.e., functions declared in an `extern {...}` block have "C" +/// ABI. +/// +/// For more information and a list of supported ABIs, see [the nomicon's +/// section on foreign calling conventions][nomicon-abi]. +/// +/// [nomicon-abi]: ../nomicon/ffi.html#foreign-calling-conventions +/// +/// ### Variadic functions +/// +/// Extern function declarations with the "C" or "cdecl" ABIs can also be *variadic*, allowing them +/// to be called with a variable number of arguments. Normal Rust functions, even those with an +/// `extern "ABI"`, cannot be variadic. For more information, see [the nomicon's section on +/// variadic functions][nomicon-variadic]. +/// +/// [nomicon-variadic]: ../nomicon/ffi.html#variadic-functions +/// +/// ### Creating function pointers +/// +/// When `bar` is the name of a function, then the expression `bar` is *not* a +/// function pointer. Rather, it denotes a value of an unnameable type that +/// uniquely identifies the function `bar`. The value is zero-sized because the +/// type already identifies the function. This has the advantage that "calling" +/// the value (it implements the `Fn*` traits) does not require dynamic +/// dispatch. +/// +/// This zero-sized type *coerces* to a regular function pointer. For example: +/// +/// ```rust +/// use std::mem; +/// +/// fn bar(x: i32) {} +/// +/// let not_bar_ptr = bar; // `not_bar_ptr` is zero-sized, uniquely identifying `bar` +/// assert_eq!(mem::size_of_val(¬_bar_ptr), 0); +/// +/// let bar_ptr: fn(i32) = not_bar_ptr; // force coercion to function pointer +/// assert_eq!(mem::size_of_val(&bar_ptr), mem::size_of::()); +/// +/// let footgun = &bar; // this is a shared reference to the zero-sized type identifying `bar` +/// ``` +/// +/// The last line shows that `&bar` is not a function pointer either. Rather, it +/// is a reference to the function-specific ZST. `&bar` is basically never what you +/// want when `bar` is a function. +/// +/// ### Casting to and from integers +/// +/// You cast function pointers directly to integers: +/// +/// ```rust +/// let fnptr: fn(i32) -> i32 = |x| x+2; +/// let fnptr_addr = fnptr as usize; +/// ``` +/// +/// However, a direct cast back is not possible. You need to use `transmute`: +/// +/// ```rust +/// # let fnptr: fn(i32) -> i32 = |x| x+2; +/// # let fnptr_addr = fnptr as usize; +/// let fnptr = fnptr_addr as *const (); +/// let fnptr: fn(i32) -> i32 = unsafe { std::mem::transmute(fnptr) }; +/// assert_eq!(fnptr(40), 42); +/// ``` +/// +/// Crucially, we `as`-cast to a raw pointer before `transmute`ing to a function pointer. +/// This avoids an integer-to-pointer `transmute`, which can be problematic. +/// Transmuting between raw pointers and function pointers (i.e., two pointer types) is fine. +/// +/// Note that all of this is not portable to platforms where function pointers and data pointers +/// have different sizes. +/// +/// ### Trait implementations +/// +/// In this documentation the shorthand `fn (T₁, T₂, …, Tₙ)` is used to represent non-variadic +/// function pointers of varying length. Note that this is a convenience notation to avoid +/// repetitive documentation, not valid Rust syntax. +/// +/// Due to a temporary restriction in Rust's type system, these traits are only implemented on +/// functions that take 12 arguments or less, with the `"Rust"` and `"C"` ABIs. In the future, this +/// may change: +/// +/// * [`PartialEq`] +/// * [`Eq`] +/// * [`PartialOrd`] +/// * [`Ord`] +/// * [`Hash`] +/// * [`Pointer`] +/// * [`Debug`] +/// +/// The following traits are implemented for function pointers with any number of arguments and +/// any ABI. These traits have implementations that are automatically generated by the compiler, +/// so are not limited by missing language features: +/// +/// * [`Clone`] +/// * [`Copy`] +/// * [`Send`] +/// * [`Sync`] +/// * [`Unpin`] +/// * [`UnwindSafe`] +/// * [`RefUnwindSafe`] +/// +/// [`Hash`]: hash::Hash +/// [`Pointer`]: fmt::Pointer +/// [`UnwindSafe`]: panic::UnwindSafe +/// [`RefUnwindSafe`]: panic::RefUnwindSafe +/// +/// In addition, all *safe* function pointers implement [`Fn`], [`FnMut`], and [`FnOnce`], because +/// these traits are specially known to the compiler. +#[stable(feature = "rust1", since = "1.0.0")] +mod prim_fn {} + +// Required to make auto trait impls render. +// See src/librustdoc/passes/collect_trait_impls.rs:collect_trait_impls +#[doc(hidden)] +#[cfg(not(bootstrap))] +impl fn(T) -> Ret {} + +// Fake impl that's only really used for docs. +#[cfg(doc)] +#[stable(feature = "rust1", since = "1.0.0")] +#[cfg_attr(not(bootstrap), doc(fake_variadic))] +/// This trait is implemented on function pointers with any number of arguments. +impl Clone for fn(T) -> Ret { + fn clone(&self) -> Self { + loop {} + } +} + +// Fake impl that's only really used for docs. +#[cfg(doc)] +#[stable(feature = "rust1", since = "1.0.0")] +#[cfg_attr(not(bootstrap), doc(fake_variadic))] +/// This trait is implemented on function pointers with any number of arguments. +impl Copy for fn(T) -> Ret { + // empty +} -- cgit v1.2.3