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Diffstat (limited to 'third_party/rust/slab/src/lib.rs')
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diff --git a/third_party/rust/slab/src/lib.rs b/third_party/rust/slab/src/lib.rs new file mode 100644 index 0000000000..e23ead9129 --- /dev/null +++ b/third_party/rust/slab/src/lib.rs @@ -0,0 +1,1571 @@ +#![cfg_attr(not(feature = "std"), no_std)] +#![warn( + missing_debug_implementations, + missing_docs, + rust_2018_idioms, + unreachable_pub +)] +#![doc(test( + no_crate_inject, + attr(deny(warnings, rust_2018_idioms), allow(dead_code, unused_variables)) +))] + +//! Pre-allocated storage for a uniform data type. +//! +//! `Slab` provides pre-allocated storage for a single data type. If many values +//! of a single type are being allocated, it can be more efficient to +//! pre-allocate the necessary storage. Since the size of the type is uniform, +//! memory fragmentation can be avoided. Storing, clearing, and lookup +//! operations become very cheap. +//! +//! While `Slab` may look like other Rust collections, it is not intended to be +//! used as a general purpose collection. The primary difference between `Slab` +//! and `Vec` is that `Slab` returns the key when storing the value. +//! +//! It is important to note that keys may be reused. In other words, once a +//! value associated with a given key is removed from a slab, that key may be +//! returned from future calls to `insert`. +//! +//! # Examples +//! +//! Basic storing and retrieval. +//! +//! ``` +//! # use slab::*; +//! let mut slab = Slab::new(); +//! +//! let hello = slab.insert("hello"); +//! let world = slab.insert("world"); +//! +//! assert_eq!(slab[hello], "hello"); +//! assert_eq!(slab[world], "world"); +//! +//! slab[world] = "earth"; +//! assert_eq!(slab[world], "earth"); +//! ``` +//! +//! Sometimes it is useful to be able to associate the key with the value being +//! inserted in the slab. This can be done with the `vacant_entry` API as such: +//! +//! ``` +//! # use slab::*; +//! let mut slab = Slab::new(); +//! +//! let hello = { +//! let entry = slab.vacant_entry(); +//! let key = entry.key(); +//! +//! entry.insert((key, "hello")); +//! key +//! }; +//! +//! assert_eq!(hello, slab[hello].0); +//! assert_eq!("hello", slab[hello].1); +//! ``` +//! +//! It is generally a good idea to specify the desired capacity of a slab at +//! creation time. Note that `Slab` will grow the internal capacity when +//! attempting to insert a new value once the existing capacity has been reached. +//! To avoid this, add a check. +//! +//! ``` +//! # use slab::*; +//! let mut slab = Slab::with_capacity(1024); +//! +//! // ... use the slab +//! +//! if slab.len() == slab.capacity() { +//! panic!("slab full"); +//! } +//! +//! slab.insert("the slab is not at capacity yet"); +//! ``` +//! +//! # Capacity and reallocation +//! +//! The capacity of a slab is the amount of space allocated for any future +//! values that will be inserted in the slab. This is not to be confused with +//! the *length* of the slab, which specifies the number of actual values +//! currently being inserted. If a slab's length is equal to its capacity, the +//! next value inserted into the slab will require growing the slab by +//! reallocating. +//! +//! For example, a slab with capacity 10 and length 0 would be an empty slab +//! with space for 10 more stored values. Storing 10 or fewer elements into the +//! slab will not change its capacity or cause reallocation to occur. However, +//! if the slab length is increased to 11 (due to another `insert`), it will +//! have to reallocate, which can be slow. For this reason, it is recommended to +//! use [`Slab::with_capacity`] whenever possible to specify how many values the +//! slab is expected to store. +//! +//! # Implementation +//! +//! `Slab` is backed by a `Vec` of slots. Each slot is either occupied or +//! vacant. `Slab` maintains a stack of vacant slots using a linked list. To +//! find a vacant slot, the stack is popped. When a slot is released, it is +//! pushed onto the stack. +//! +//! If there are no more available slots in the stack, then `Vec::reserve(1)` is +//! called and a new slot is created. +//! +//! [`Slab::with_capacity`]: struct.Slab.html#with_capacity + +#[cfg(not(feature = "std"))] +extern crate alloc; +#[cfg(feature = "std")] +extern crate std as alloc; + +#[cfg(feature = "serde")] +mod serde; + +mod builder; + +use alloc::vec::{self, Vec}; +use core::iter::{self, FromIterator, FusedIterator}; +use core::{fmt, mem, ops, slice}; + +/// Pre-allocated storage for a uniform data type +/// +/// See the [module documentation] for more details. +/// +/// [module documentation]: index.html +#[derive(Clone)] +pub struct Slab<T> { + // Chunk of memory + entries: Vec<Entry<T>>, + + // Number of Filled elements currently in the slab + len: usize, + + // Offset of the next available slot in the slab. Set to the slab's + // capacity when the slab is full. + next: usize, +} + +impl<T> Default for Slab<T> { + fn default() -> Self { + Slab::new() + } +} + +/// A handle to a vacant entry in a `Slab`. +/// +/// `VacantEntry` allows constructing values with the key that they will be +/// assigned to. +/// +/// # Examples +/// +/// ``` +/// # use slab::*; +/// let mut slab = Slab::new(); +/// +/// let hello = { +/// let entry = slab.vacant_entry(); +/// let key = entry.key(); +/// +/// entry.insert((key, "hello")); +/// key +/// }; +/// +/// assert_eq!(hello, slab[hello].0); +/// assert_eq!("hello", slab[hello].1); +/// ``` +#[derive(Debug)] +pub struct VacantEntry<'a, T> { + slab: &'a mut Slab<T>, + key: usize, +} + +/// A consuming iterator over the values stored in a `Slab` +pub struct IntoIter<T> { + entries: iter::Enumerate<vec::IntoIter<Entry<T>>>, + len: usize, +} + +/// An iterator over the values stored in the `Slab` +pub struct Iter<'a, T> { + entries: iter::Enumerate<slice::Iter<'a, Entry<T>>>, + len: usize, +} + +impl<'a, T> Clone for Iter<'a, T> { + fn clone(&self) -> Self { + Self { + entries: self.entries.clone(), + len: self.len, + } + } +} + +/// A mutable iterator over the values stored in the `Slab` +pub struct IterMut<'a, T> { + entries: iter::Enumerate<slice::IterMut<'a, Entry<T>>>, + len: usize, +} + +/// A draining iterator for `Slab` +pub struct Drain<'a, T> { + inner: vec::Drain<'a, Entry<T>>, + len: usize, +} + +#[derive(Clone)] +enum Entry<T> { + Vacant(usize), + Occupied(T), +} + +impl<T> Slab<T> { + /// Construct a new, empty `Slab`. + /// + /// The function does not allocate and the returned slab will have no + /// capacity until `insert` is called or capacity is explicitly reserved. + /// + /// This is `const fn` on Rust 1.39+. + /// + /// # Examples + /// + /// ``` + /// # use slab::*; + /// let slab: Slab<i32> = Slab::new(); + /// ``` + #[cfg(not(slab_no_const_vec_new))] + pub const fn new() -> Self { + Self { + entries: Vec::new(), + next: 0, + len: 0, + } + } + /// Construct a new, empty `Slab`. + /// + /// The function does not allocate and the returned slab will have no + /// capacity until `insert` is called or capacity is explicitly reserved. + /// + /// This is `const fn` on Rust 1.39+. + #[cfg(slab_no_const_vec_new)] + pub fn new() -> Self { + Self { + entries: Vec::new(), + next: 0, + len: 0, + } + } + + /// Construct a new, empty `Slab` with the specified capacity. + /// + /// The returned slab will be able to store exactly `capacity` without + /// reallocating. If `capacity` is 0, the slab will not allocate. + /// + /// It is important to note that this function does not specify the *length* + /// of the returned slab, but only the capacity. For an explanation of the + /// difference between length and capacity, see [Capacity and + /// reallocation](index.html#capacity-and-reallocation). + /// + /// # Examples + /// + /// ``` + /// # use slab::*; + /// let mut slab = Slab::with_capacity(10); + /// + /// // The slab contains no values, even though it has capacity for more + /// assert_eq!(slab.len(), 0); + /// + /// // These are all done without reallocating... + /// for i in 0..10 { + /// slab.insert(i); + /// } + /// + /// // ...but this may make the slab reallocate + /// slab.insert(11); + /// ``` + pub fn with_capacity(capacity: usize) -> Slab<T> { + Slab { + entries: Vec::with_capacity(capacity), + next: 0, + len: 0, + } + } + + /// Return the number of values the slab can store without reallocating. + /// + /// # Examples + /// + /// ``` + /// # use slab::*; + /// let slab: Slab<i32> = Slab::with_capacity(10); + /// assert_eq!(slab.capacity(), 10); + /// ``` + pub fn capacity(&self) -> usize { + self.entries.capacity() + } + + /// Reserve capacity for at least `additional` more values to be stored + /// without allocating. + /// + /// `reserve` does nothing if the slab already has sufficient capacity for + /// `additional` more values. If more capacity is required, a new segment of + /// memory will be allocated and all existing values will be copied into it. + /// As such, if the slab is already very large, a call to `reserve` can end + /// up being expensive. + /// + /// The slab may reserve more than `additional` extra space in order to + /// avoid frequent reallocations. Use `reserve_exact` instead to guarantee + /// that only the requested space is allocated. + /// + /// # Panics + /// + /// Panics if the new capacity exceeds `isize::MAX` bytes. + /// + /// # Examples + /// + /// ``` + /// # use slab::*; + /// let mut slab = Slab::new(); + /// slab.insert("hello"); + /// slab.reserve(10); + /// assert!(slab.capacity() >= 11); + /// ``` + pub fn reserve(&mut self, additional: usize) { + if self.capacity() - self.len >= additional { + return; + } + let need_add = additional - (self.entries.len() - self.len); + self.entries.reserve(need_add); + } + + /// Reserve the minimum capacity required to store exactly `additional` + /// more values. + /// + /// `reserve_exact` does nothing if the slab already has sufficient capacity + /// for `additional` more values. If more capacity is required, a new segment + /// of memory will be allocated and all existing values will be copied into + /// it. As such, if the slab is already very large, a call to `reserve` can + /// end up being expensive. + /// + /// Note that the allocator may give the slab more space than it requests. + /// Therefore capacity can not be relied upon to be precisely minimal. + /// Prefer `reserve` if future insertions are expected. + /// + /// # Panics + /// + /// Panics if the new capacity exceeds `isize::MAX` bytes. + /// + /// # Examples + /// + /// ``` + /// # use slab::*; + /// let mut slab = Slab::new(); + /// slab.insert("hello"); + /// slab.reserve_exact(10); + /// assert!(slab.capacity() >= 11); + /// ``` + pub fn reserve_exact(&mut self, additional: usize) { + if self.capacity() - self.len >= additional { + return; + } + let need_add = additional - (self.entries.len() - self.len); + self.entries.reserve_exact(need_add); + } + + /// Shrink the capacity of the slab as much as possible without invalidating keys. + /// + /// Because values cannot be moved to a different index, the slab cannot + /// shrink past any stored values. + /// It will drop down as close as possible to the length but the allocator may + /// still inform the underlying vector that there is space for a few more elements. + /// + /// This function can take O(n) time even when the capacity cannot be reduced + /// or the allocation is shrunk in place. Repeated calls run in O(1) though. + /// + /// # Examples + /// + /// ``` + /// # use slab::*; + /// let mut slab = Slab::with_capacity(10); + /// + /// for i in 0..3 { + /// slab.insert(i); + /// } + /// + /// slab.shrink_to_fit(); + /// assert!(slab.capacity() >= 3 && slab.capacity() < 10); + /// ``` + /// + /// The slab cannot shrink past the last present value even if previous + /// values are removed: + /// + /// ``` + /// # use slab::*; + /// let mut slab = Slab::with_capacity(10); + /// + /// for i in 0..4 { + /// slab.insert(i); + /// } + /// + /// slab.remove(0); + /// slab.remove(3); + /// + /// slab.shrink_to_fit(); + /// assert!(slab.capacity() >= 3 && slab.capacity() < 10); + /// ``` + pub fn shrink_to_fit(&mut self) { + // Remove all vacant entries after the last occupied one, so that + // the capacity can be reduced to what is actually needed. + // If the slab is empty the vector can simply be cleared, but that + // optimization would not affect time complexity when T: Drop. + let len_before = self.entries.len(); + while let Some(&Entry::Vacant(_)) = self.entries.last() { + self.entries.pop(); + } + + // Removing entries breaks the list of vacant entries, + // so it must be repaired + if self.entries.len() != len_before { + // Some vacant entries were removed, so the list now likely¹ + // either contains references to the removed entries, or has an + // invalid end marker. Fix this by recreating the list. + self.recreate_vacant_list(); + // ¹: If the removed entries formed the tail of the list, with the + // most recently popped entry being the head of them, (so that its + // index is now the end marker) the list is still valid. + // Checking for that unlikely scenario of this infrequently called + // is not worth the code complexity. + } + + self.entries.shrink_to_fit(); + } + + /// Iterate through all entries to recreate and repair the vacant list. + /// self.len must be correct and is not modified. + fn recreate_vacant_list(&mut self) { + self.next = self.entries.len(); + // We can stop once we've found all vacant entries + let mut remaining_vacant = self.entries.len() - self.len; + if remaining_vacant == 0 { + return; + } + + // Iterate in reverse order so that lower keys are at the start of + // the vacant list. This way future shrinks are more likely to be + // able to remove vacant entries. + for (i, entry) in self.entries.iter_mut().enumerate().rev() { + if let Entry::Vacant(ref mut next) = *entry { + *next = self.next; + self.next = i; + remaining_vacant -= 1; + if remaining_vacant == 0 { + break; + } + } + } + } + + /// Reduce the capacity as much as possible, changing the key for elements when necessary. + /// + /// To allow updating references to the elements which must be moved to a new key, + /// this function takes a closure which is called before moving each element. + /// The second and third parameters to the closure are the current key and + /// new key respectively. + /// In case changing the key for one element turns out not to be possible, + /// the move can be cancelled by returning `false` from the closure. + /// In that case no further attempts at relocating elements is made. + /// If the closure unwinds, the slab will be left in a consistent state, + /// but the value that the closure panicked on might be removed. + /// + /// # Examples + /// + /// ``` + /// # use slab::*; + /// + /// let mut slab = Slab::with_capacity(10); + /// let a = slab.insert('a'); + /// slab.insert('b'); + /// slab.insert('c'); + /// slab.remove(a); + /// slab.compact(|&mut value, from, to| { + /// assert_eq!((value, from, to), ('c', 2, 0)); + /// true + /// }); + /// assert!(slab.capacity() >= 2 && slab.capacity() < 10); + /// ``` + /// + /// The value is not moved when the closure returns `Err`: + /// + /// ``` + /// # use slab::*; + /// + /// let mut slab = Slab::with_capacity(100); + /// let a = slab.insert('a'); + /// let b = slab.insert('b'); + /// slab.remove(a); + /// slab.compact(|&mut value, from, to| false); + /// assert_eq!(slab.iter().next(), Some((b, &'b'))); + /// ``` + pub fn compact<F>(&mut self, mut rekey: F) + where + F: FnMut(&mut T, usize, usize) -> bool, + { + // If the closure unwinds, we need to restore a valid list of vacant entries + struct CleanupGuard<'a, T> { + slab: &'a mut Slab<T>, + decrement: bool, + } + impl<T> Drop for CleanupGuard<'_, T> { + fn drop(&mut self) { + if self.decrement { + // Value was popped and not pushed back on + self.slab.len -= 1; + } + self.slab.recreate_vacant_list(); + } + } + let mut guard = CleanupGuard { + slab: self, + decrement: true, + }; + + let mut occupied_until = 0; + // While there are vacant entries + while guard.slab.entries.len() > guard.slab.len { + // Find a value that needs to be moved, + // by popping entries until we find an occupied one. + // (entries cannot be empty because 0 is not greater than anything) + if let Some(Entry::Occupied(mut value)) = guard.slab.entries.pop() { + // Found one, now find a vacant entry to move it to + while let Some(&Entry::Occupied(_)) = guard.slab.entries.get(occupied_until) { + occupied_until += 1; + } + // Let the caller try to update references to the key + if !rekey(&mut value, guard.slab.entries.len(), occupied_until) { + // Changing the key failed, so push the entry back on at its old index. + guard.slab.entries.push(Entry::Occupied(value)); + guard.decrement = false; + guard.slab.entries.shrink_to_fit(); + return; + // Guard drop handles cleanup + } + // Put the value in its new spot + guard.slab.entries[occupied_until] = Entry::Occupied(value); + // ... and mark it as occupied (this is optional) + occupied_until += 1; + } + } + guard.slab.next = guard.slab.len; + guard.slab.entries.shrink_to_fit(); + // Normal cleanup is not necessary + mem::forget(guard); + } + + /// Clear the slab of all values. + /// + /// # Examples + /// + /// ``` + /// # use slab::*; + /// let mut slab = Slab::new(); + /// + /// for i in 0..3 { + /// slab.insert(i); + /// } + /// + /// slab.clear(); + /// assert!(slab.is_empty()); + /// ``` + pub fn clear(&mut self) { + self.entries.clear(); + self.len = 0; + self.next = 0; + } + + /// Return the number of stored values. + /// + /// # Examples + /// + /// ``` + /// # use slab::*; + /// let mut slab = Slab::new(); + /// + /// for i in 0..3 { + /// slab.insert(i); + /// } + /// + /// assert_eq!(3, slab.len()); + /// ``` + pub fn len(&self) -> usize { + self.len + } + + /// Return `true` if there are no values stored in the slab. + /// + /// # Examples + /// + /// ``` + /// # use slab::*; + /// let mut slab = Slab::new(); + /// assert!(slab.is_empty()); + /// + /// slab.insert(1); + /// assert!(!slab.is_empty()); + /// ``` + pub fn is_empty(&self) -> bool { + self.len == 0 + } + + /// Return an iterator over the slab. + /// + /// This function should generally be **avoided** as it is not efficient. + /// Iterators must iterate over every slot in the slab even if it is + /// vacant. As such, a slab with a capacity of 1 million but only one + /// stored value must still iterate the million slots. + /// + /// # Examples + /// + /// ``` + /// # use slab::*; + /// let mut slab = Slab::new(); + /// + /// for i in 0..3 { + /// slab.insert(i); + /// } + /// + /// let mut iterator = slab.iter(); + /// + /// assert_eq!(iterator.next(), Some((0, &0))); + /// assert_eq!(iterator.next(), Some((1, &1))); + /// assert_eq!(iterator.next(), Some((2, &2))); + /// assert_eq!(iterator.next(), None); + /// ``` + pub fn iter(&self) -> Iter<'_, T> { + Iter { + entries: self.entries.iter().enumerate(), + len: self.len, + } + } + + /// Return an iterator that allows modifying each value. + /// + /// This function should generally be **avoided** as it is not efficient. + /// Iterators must iterate over every slot in the slab even if it is + /// vacant. As such, a slab with a capacity of 1 million but only one + /// stored value must still iterate the million slots. + /// + /// # Examples + /// + /// ``` + /// # use slab::*; + /// let mut slab = Slab::new(); + /// + /// let key1 = slab.insert(0); + /// let key2 = slab.insert(1); + /// + /// for (key, val) in slab.iter_mut() { + /// if key == key1 { + /// *val += 2; + /// } + /// } + /// + /// assert_eq!(slab[key1], 2); + /// assert_eq!(slab[key2], 1); + /// ``` + pub fn iter_mut(&mut self) -> IterMut<'_, T> { + IterMut { + entries: self.entries.iter_mut().enumerate(), + len: self.len, + } + } + + /// Return a reference to the value associated with the given key. + /// + /// If the given key is not associated with a value, then `None` is + /// returned. + /// + /// # Examples + /// + /// ``` + /// # use slab::*; + /// let mut slab = Slab::new(); + /// let key = slab.insert("hello"); + /// + /// assert_eq!(slab.get(key), Some(&"hello")); + /// assert_eq!(slab.get(123), None); + /// ``` + pub fn get(&self, key: usize) -> Option<&T> { + match self.entries.get(key) { + Some(Entry::Occupied(val)) => Some(val), + _ => None, + } + } + + /// Return a mutable reference to the value associated with the given key. + /// + /// If the given key is not associated with a value, then `None` is + /// returned. + /// + /// # Examples + /// + /// ``` + /// # use slab::*; + /// let mut slab = Slab::new(); + /// let key = slab.insert("hello"); + /// + /// *slab.get_mut(key).unwrap() = "world"; + /// + /// assert_eq!(slab[key], "world"); + /// assert_eq!(slab.get_mut(123), None); + /// ``` + pub fn get_mut(&mut self, key: usize) -> Option<&mut T> { + match self.entries.get_mut(key) { + Some(&mut Entry::Occupied(ref mut val)) => Some(val), + _ => None, + } + } + + /// Return two mutable references to the values associated with the two + /// given keys simultaneously. + /// + /// If any one of the given keys is not associated with a value, then `None` + /// is returned. + /// + /// This function can be used to get two mutable references out of one slab, + /// so that you can manipulate both of them at the same time, eg. swap them. + /// + /// # Panics + /// + /// This function will panic if `key1` and `key2` are the same. + /// + /// # Examples + /// + /// ``` + /// # use slab::*; + /// use std::mem; + /// + /// let mut slab = Slab::new(); + /// let key1 = slab.insert(1); + /// let key2 = slab.insert(2); + /// let (value1, value2) = slab.get2_mut(key1, key2).unwrap(); + /// mem::swap(value1, value2); + /// assert_eq!(slab[key1], 2); + /// assert_eq!(slab[key2], 1); + /// ``` + pub fn get2_mut(&mut self, key1: usize, key2: usize) -> Option<(&mut T, &mut T)> { + assert!(key1 != key2); + + let (entry1, entry2); + + if key1 > key2 { + let (slice1, slice2) = self.entries.split_at_mut(key1); + entry1 = slice2.get_mut(0); + entry2 = slice1.get_mut(key2); + } else { + let (slice1, slice2) = self.entries.split_at_mut(key2); + entry1 = slice1.get_mut(key1); + entry2 = slice2.get_mut(0); + } + + match (entry1, entry2) { + ( + Some(&mut Entry::Occupied(ref mut val1)), + Some(&mut Entry::Occupied(ref mut val2)), + ) => Some((val1, val2)), + _ => None, + } + } + + /// Return a reference to the value associated with the given key without + /// performing bounds checking. + /// + /// For a safe alternative see [`get`](Slab::get). + /// + /// This function should be used with care. + /// + /// # Safety + /// + /// The key must be within bounds. + /// + /// # Examples + /// + /// ``` + /// # use slab::*; + /// let mut slab = Slab::new(); + /// let key = slab.insert(2); + /// + /// unsafe { + /// assert_eq!(slab.get_unchecked(key), &2); + /// } + /// ``` + pub unsafe fn get_unchecked(&self, key: usize) -> &T { + match *self.entries.get_unchecked(key) { + Entry::Occupied(ref val) => val, + _ => unreachable!(), + } + } + + /// Return a mutable reference to the value associated with the given key + /// without performing bounds checking. + /// + /// For a safe alternative see [`get_mut`](Slab::get_mut). + /// + /// This function should be used with care. + /// + /// # Safety + /// + /// The key must be within bounds. + /// + /// # Examples + /// + /// ``` + /// # use slab::*; + /// let mut slab = Slab::new(); + /// let key = slab.insert(2); + /// + /// unsafe { + /// let val = slab.get_unchecked_mut(key); + /// *val = 13; + /// } + /// + /// assert_eq!(slab[key], 13); + /// ``` + pub unsafe fn get_unchecked_mut(&mut self, key: usize) -> &mut T { + match *self.entries.get_unchecked_mut(key) { + Entry::Occupied(ref mut val) => val, + _ => unreachable!(), + } + } + + /// Return two mutable references to the values associated with the two + /// given keys simultaneously without performing bounds checking and safety + /// condition checking. + /// + /// For a safe alternative see [`get2_mut`](Slab::get2_mut). + /// + /// This function should be used with care. + /// + /// # Safety + /// + /// - Both keys must be within bounds. + /// - The condition `key1 != key2` must hold. + /// + /// # Examples + /// + /// ``` + /// # use slab::*; + /// use std::mem; + /// + /// let mut slab = Slab::new(); + /// let key1 = slab.insert(1); + /// let key2 = slab.insert(2); + /// let (value1, value2) = unsafe { slab.get2_unchecked_mut(key1, key2) }; + /// mem::swap(value1, value2); + /// assert_eq!(slab[key1], 2); + /// assert_eq!(slab[key2], 1); + /// ``` + pub unsafe fn get2_unchecked_mut(&mut self, key1: usize, key2: usize) -> (&mut T, &mut T) { + debug_assert_ne!(key1, key2); + let ptr = self.entries.as_mut_ptr(); + let ptr1 = ptr.add(key1); + let ptr2 = ptr.add(key2); + match (&mut *ptr1, &mut *ptr2) { + (&mut Entry::Occupied(ref mut val1), &mut Entry::Occupied(ref mut val2)) => { + (val1, val2) + } + _ => unreachable!(), + } + } + + /// Get the key for an element in the slab. + /// + /// The reference must point to an element owned by the slab. + /// Otherwise this function will panic. + /// This is a constant-time operation because the key can be calculated + /// from the reference with pointer arithmetic. + /// + /// # Panics + /// + /// This function will panic if the reference does not point to an element + /// of the slab. + /// + /// # Examples + /// + /// ``` + /// # use slab::*; + /// + /// let mut slab = Slab::new(); + /// let key = slab.insert(String::from("foo")); + /// let value = &slab[key]; + /// assert_eq!(slab.key_of(value), key); + /// ``` + /// + /// Values are not compared, so passing a reference to a different location + /// will result in a panic: + /// + /// ```should_panic + /// # use slab::*; + /// + /// let mut slab = Slab::new(); + /// let key = slab.insert(0); + /// let bad = &0; + /// slab.key_of(bad); // this will panic + /// unreachable!(); + /// ``` + #[cfg_attr(not(slab_no_track_caller), track_caller)] + pub fn key_of(&self, present_element: &T) -> usize { + let element_ptr = present_element as *const T as usize; + let base_ptr = self.entries.as_ptr() as usize; + // Use wrapping subtraction in case the reference is bad + let byte_offset = element_ptr.wrapping_sub(base_ptr); + // The division rounds away any offset of T inside Entry + // The size of Entry<T> is never zero even if T is due to Vacant(usize) + let key = byte_offset / mem::size_of::<Entry<T>>(); + // Prevent returning unspecified (but out of bounds) values + if key >= self.entries.len() { + panic!("The reference points to a value outside this slab"); + } + // The reference cannot point to a vacant entry, because then it would not be valid + key + } + + /// Insert a value in the slab, returning key assigned to the value. + /// + /// The returned key can later be used to retrieve or remove the value using indexed + /// lookup and `remove`. Additional capacity is allocated if needed. See + /// [Capacity and reallocation](index.html#capacity-and-reallocation). + /// + /// # Panics + /// + /// Panics if the new storage in the vector exceeds `isize::MAX` bytes. + /// + /// # Examples + /// + /// ``` + /// # use slab::*; + /// let mut slab = Slab::new(); + /// let key = slab.insert("hello"); + /// assert_eq!(slab[key], "hello"); + /// ``` + pub fn insert(&mut self, val: T) -> usize { + let key = self.next; + + self.insert_at(key, val); + + key + } + + /// Returns the key of the next vacant entry. + /// + /// This function returns the key of the vacant entry which will be used + /// for the next insertion. This is equivalent to + /// `slab.vacant_entry().key()`, but it doesn't require mutable access. + /// + /// # Examples + /// + /// ``` + /// # use slab::*; + /// let mut slab = Slab::new(); + /// assert_eq!(slab.vacant_key(), 0); + /// + /// slab.insert(0); + /// assert_eq!(slab.vacant_key(), 1); + /// + /// slab.insert(1); + /// slab.remove(0); + /// assert_eq!(slab.vacant_key(), 0); + /// ``` + pub fn vacant_key(&self) -> usize { + self.next + } + + /// Return a handle to a vacant entry allowing for further manipulation. + /// + /// This function is useful when creating values that must contain their + /// slab key. The returned `VacantEntry` reserves a slot in the slab and is + /// able to query the associated key. + /// + /// # Examples + /// + /// ``` + /// # use slab::*; + /// let mut slab = Slab::new(); + /// + /// let hello = { + /// let entry = slab.vacant_entry(); + /// let key = entry.key(); + /// + /// entry.insert((key, "hello")); + /// key + /// }; + /// + /// assert_eq!(hello, slab[hello].0); + /// assert_eq!("hello", slab[hello].1); + /// ``` + pub fn vacant_entry(&mut self) -> VacantEntry<'_, T> { + VacantEntry { + key: self.next, + slab: self, + } + } + + fn insert_at(&mut self, key: usize, val: T) { + self.len += 1; + + if key == self.entries.len() { + self.entries.push(Entry::Occupied(val)); + self.next = key + 1; + } else { + self.next = match self.entries.get(key) { + Some(&Entry::Vacant(next)) => next, + _ => unreachable!(), + }; + self.entries[key] = Entry::Occupied(val); + } + } + + /// Tries to remove the value associated with the given key, + /// returning the value if the key existed. + /// + /// The key is then released and may be associated with future stored + /// values. + /// + /// # Examples + /// + /// ``` + /// # use slab::*; + /// let mut slab = Slab::new(); + /// + /// let hello = slab.insert("hello"); + /// + /// assert_eq!(slab.try_remove(hello), Some("hello")); + /// assert!(!slab.contains(hello)); + /// ``` + pub fn try_remove(&mut self, key: usize) -> Option<T> { + if let Some(entry) = self.entries.get_mut(key) { + // Swap the entry at the provided value + let prev = mem::replace(entry, Entry::Vacant(self.next)); + + match prev { + Entry::Occupied(val) => { + self.len -= 1; + self.next = key; + return val.into(); + } + _ => { + // Woops, the entry is actually vacant, restore the state + *entry = prev; + } + } + } + None + } + + /// Remove and return the value associated with the given key. + /// + /// The key is then released and may be associated with future stored + /// values. + /// + /// # Panics + /// + /// Panics if `key` is not associated with a value. + /// + /// # Examples + /// + /// ``` + /// # use slab::*; + /// let mut slab = Slab::new(); + /// + /// let hello = slab.insert("hello"); + /// + /// assert_eq!(slab.remove(hello), "hello"); + /// assert!(!slab.contains(hello)); + /// ``` + #[cfg_attr(not(slab_no_track_caller), track_caller)] + pub fn remove(&mut self, key: usize) -> T { + self.try_remove(key).expect("invalid key") + } + + /// Return `true` if a value is associated with the given key. + /// + /// # Examples + /// + /// ``` + /// # use slab::*; + /// let mut slab = Slab::new(); + /// + /// let hello = slab.insert("hello"); + /// assert!(slab.contains(hello)); + /// + /// slab.remove(hello); + /// + /// assert!(!slab.contains(hello)); + /// ``` + pub fn contains(&self, key: usize) -> bool { + match self.entries.get(key) { + Some(&Entry::Occupied(_)) => true, + _ => false, + } + } + + /// Retain only the elements specified by the predicate. + /// + /// In other words, remove all elements `e` such that `f(usize, &mut e)` + /// returns false. This method operates in place and preserves the key + /// associated with the retained values. + /// + /// # Examples + /// + /// ``` + /// # use slab::*; + /// let mut slab = Slab::new(); + /// + /// let k1 = slab.insert(0); + /// let k2 = slab.insert(1); + /// let k3 = slab.insert(2); + /// + /// slab.retain(|key, val| key == k1 || *val == 1); + /// + /// assert!(slab.contains(k1)); + /// assert!(slab.contains(k2)); + /// assert!(!slab.contains(k3)); + /// + /// assert_eq!(2, slab.len()); + /// ``` + pub fn retain<F>(&mut self, mut f: F) + where + F: FnMut(usize, &mut T) -> bool, + { + for i in 0..self.entries.len() { + let keep = match self.entries[i] { + Entry::Occupied(ref mut v) => f(i, v), + _ => true, + }; + + if !keep { + self.remove(i); + } + } + } + + /// Return a draining iterator that removes all elements from the slab and + /// yields the removed items. + /// + /// Note: Elements are removed even if the iterator is only partially + /// consumed or not consumed at all. + /// + /// # Examples + /// + /// ``` + /// # use slab::*; + /// let mut slab = Slab::new(); + /// + /// let _ = slab.insert(0); + /// let _ = slab.insert(1); + /// let _ = slab.insert(2); + /// + /// { + /// let mut drain = slab.drain(); + /// + /// assert_eq!(Some(0), drain.next()); + /// assert_eq!(Some(1), drain.next()); + /// assert_eq!(Some(2), drain.next()); + /// assert_eq!(None, drain.next()); + /// } + /// + /// assert!(slab.is_empty()); + /// ``` + pub fn drain(&mut self) -> Drain<'_, T> { + let old_len = self.len; + self.len = 0; + self.next = 0; + Drain { + inner: self.entries.drain(..), + len: old_len, + } + } +} + +impl<T> ops::Index<usize> for Slab<T> { + type Output = T; + + #[cfg_attr(not(slab_no_track_caller), track_caller)] + fn index(&self, key: usize) -> &T { + match self.entries.get(key) { + Some(Entry::Occupied(v)) => v, + _ => panic!("invalid key"), + } + } +} + +impl<T> ops::IndexMut<usize> for Slab<T> { + #[cfg_attr(not(slab_no_track_caller), track_caller)] + fn index_mut(&mut self, key: usize) -> &mut T { + match self.entries.get_mut(key) { + Some(&mut Entry::Occupied(ref mut v)) => v, + _ => panic!("invalid key"), + } + } +} + +impl<T> IntoIterator for Slab<T> { + type Item = (usize, T); + type IntoIter = IntoIter<T>; + + fn into_iter(self) -> IntoIter<T> { + IntoIter { + entries: self.entries.into_iter().enumerate(), + len: self.len, + } + } +} + +impl<'a, T> IntoIterator for &'a Slab<T> { + type Item = (usize, &'a T); + type IntoIter = Iter<'a, T>; + + fn into_iter(self) -> Iter<'a, T> { + self.iter() + } +} + +impl<'a, T> IntoIterator for &'a mut Slab<T> { + type Item = (usize, &'a mut T); + type IntoIter = IterMut<'a, T>; + + fn into_iter(self) -> IterMut<'a, T> { + self.iter_mut() + } +} + +/// Create a slab from an iterator of key-value pairs. +/// +/// If the iterator produces duplicate keys, the previous value is replaced with the later one. +/// The keys does not need to be sorted beforehand, and this function always +/// takes O(n) time. +/// Note that the returned slab will use space proportional to the largest key, +/// so don't use `Slab` with untrusted keys. +/// +/// # Examples +/// +/// ``` +/// # use slab::*; +/// +/// let vec = vec![(2,'a'), (6,'b'), (7,'c')]; +/// let slab = vec.into_iter().collect::<Slab<char>>(); +/// assert_eq!(slab.len(), 3); +/// assert!(slab.capacity() >= 8); +/// assert_eq!(slab[2], 'a'); +/// ``` +/// +/// With duplicate and unsorted keys: +/// +/// ``` +/// # use slab::*; +/// +/// let vec = vec![(20,'a'), (10,'b'), (11,'c'), (10,'d')]; +/// let slab = vec.into_iter().collect::<Slab<char>>(); +/// assert_eq!(slab.len(), 3); +/// assert_eq!(slab[10], 'd'); +/// ``` +impl<T> FromIterator<(usize, T)> for Slab<T> { + fn from_iter<I>(iterable: I) -> Self + where + I: IntoIterator<Item = (usize, T)>, + { + let iterator = iterable.into_iter(); + let mut builder = builder::Builder::with_capacity(iterator.size_hint().0); + + for (key, value) in iterator { + builder.pair(key, value) + } + builder.build() + } +} + +impl<T> fmt::Debug for Slab<T> +where + T: fmt::Debug, +{ + fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result { + if fmt.alternate() { + fmt.debug_map().entries(self.iter()).finish() + } else { + fmt.debug_struct("Slab") + .field("len", &self.len) + .field("cap", &self.capacity()) + .finish() + } + } +} + +impl<T> fmt::Debug for IntoIter<T> +where + T: fmt::Debug, +{ + fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result { + fmt.debug_struct("IntoIter") + .field("remaining", &self.len) + .finish() + } +} + +impl<T> fmt::Debug for Iter<'_, T> +where + T: fmt::Debug, +{ + fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result { + fmt.debug_struct("Iter") + .field("remaining", &self.len) + .finish() + } +} + +impl<T> fmt::Debug for IterMut<'_, T> +where + T: fmt::Debug, +{ + fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result { + fmt.debug_struct("IterMut") + .field("remaining", &self.len) + .finish() + } +} + +impl<T> fmt::Debug for Drain<'_, T> { + fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result { + fmt.debug_struct("Drain").finish() + } +} + +// ===== VacantEntry ===== + +impl<'a, T> VacantEntry<'a, T> { + /// Insert a value in the entry, returning a mutable reference to the value. + /// + /// To get the key associated with the value, use `key` prior to calling + /// `insert`. + /// + /// # Examples + /// + /// ``` + /// # use slab::*; + /// let mut slab = Slab::new(); + /// + /// let hello = { + /// let entry = slab.vacant_entry(); + /// let key = entry.key(); + /// + /// entry.insert((key, "hello")); + /// key + /// }; + /// + /// assert_eq!(hello, slab[hello].0); + /// assert_eq!("hello", slab[hello].1); + /// ``` + pub fn insert(self, val: T) -> &'a mut T { + self.slab.insert_at(self.key, val); + + match self.slab.entries.get_mut(self.key) { + Some(&mut Entry::Occupied(ref mut v)) => v, + _ => unreachable!(), + } + } + + /// Return the key associated with this entry. + /// + /// A value stored in this entry will be associated with this key. + /// + /// # Examples + /// + /// ``` + /// # use slab::*; + /// let mut slab = Slab::new(); + /// + /// let hello = { + /// let entry = slab.vacant_entry(); + /// let key = entry.key(); + /// + /// entry.insert((key, "hello")); + /// key + /// }; + /// + /// assert_eq!(hello, slab[hello].0); + /// assert_eq!("hello", slab[hello].1); + /// ``` + pub fn key(&self) -> usize { + self.key + } +} + +// ===== IntoIter ===== + +impl<T> Iterator for IntoIter<T> { + type Item = (usize, T); + + fn next(&mut self) -> Option<Self::Item> { + for (key, entry) in &mut self.entries { + if let Entry::Occupied(v) = entry { + self.len -= 1; + return Some((key, v)); + } + } + + debug_assert_eq!(self.len, 0); + None + } + + fn size_hint(&self) -> (usize, Option<usize>) { + (self.len, Some(self.len)) + } +} + +impl<T> DoubleEndedIterator for IntoIter<T> { + fn next_back(&mut self) -> Option<Self::Item> { + while let Some((key, entry)) = self.entries.next_back() { + if let Entry::Occupied(v) = entry { + self.len -= 1; + return Some((key, v)); + } + } + + debug_assert_eq!(self.len, 0); + None + } +} + +impl<T> ExactSizeIterator for IntoIter<T> { + fn len(&self) -> usize { + self.len + } +} + +impl<T> FusedIterator for IntoIter<T> {} + +// ===== Iter ===== + +impl<'a, T> Iterator for Iter<'a, T> { + type Item = (usize, &'a T); + + fn next(&mut self) -> Option<Self::Item> { + for (key, entry) in &mut self.entries { + if let Entry::Occupied(ref v) = *entry { + self.len -= 1; + return Some((key, v)); + } + } + + debug_assert_eq!(self.len, 0); + None + } + + fn size_hint(&self) -> (usize, Option<usize>) { + (self.len, Some(self.len)) + } +} + +impl<T> DoubleEndedIterator for Iter<'_, T> { + fn next_back(&mut self) -> Option<Self::Item> { + while let Some((key, entry)) = self.entries.next_back() { + if let Entry::Occupied(ref v) = *entry { + self.len -= 1; + return Some((key, v)); + } + } + + debug_assert_eq!(self.len, 0); + None + } +} + +impl<T> ExactSizeIterator for Iter<'_, T> { + fn len(&self) -> usize { + self.len + } +} + +impl<T> FusedIterator for Iter<'_, T> {} + +// ===== IterMut ===== + +impl<'a, T> Iterator for IterMut<'a, T> { + type Item = (usize, &'a mut T); + + fn next(&mut self) -> Option<Self::Item> { + for (key, entry) in &mut self.entries { + if let Entry::Occupied(ref mut v) = *entry { + self.len -= 1; + return Some((key, v)); + } + } + + debug_assert_eq!(self.len, 0); + None + } + + fn size_hint(&self) -> (usize, Option<usize>) { + (self.len, Some(self.len)) + } +} + +impl<T> DoubleEndedIterator for IterMut<'_, T> { + fn next_back(&mut self) -> Option<Self::Item> { + while let Some((key, entry)) = self.entries.next_back() { + if let Entry::Occupied(ref mut v) = *entry { + self.len -= 1; + return Some((key, v)); + } + } + + debug_assert_eq!(self.len, 0); + None + } +} + +impl<T> ExactSizeIterator for IterMut<'_, T> { + fn len(&self) -> usize { + self.len + } +} + +impl<T> FusedIterator for IterMut<'_, T> {} + +// ===== Drain ===== + +impl<T> Iterator for Drain<'_, T> { + type Item = T; + + fn next(&mut self) -> Option<Self::Item> { + for entry in &mut self.inner { + if let Entry::Occupied(v) = entry { + self.len -= 1; + return Some(v); + } + } + + debug_assert_eq!(self.len, 0); + None + } + + fn size_hint(&self) -> (usize, Option<usize>) { + (self.len, Some(self.len)) + } +} + +impl<T> DoubleEndedIterator for Drain<'_, T> { + fn next_back(&mut self) -> Option<Self::Item> { + while let Some(entry) = self.inner.next_back() { + if let Entry::Occupied(v) = entry { + self.len -= 1; + return Some(v); + } + } + + debug_assert_eq!(self.len, 0); + None + } +} + +impl<T> ExactSizeIterator for Drain<'_, T> { + fn len(&self) -> usize { + self.len + } +} + +impl<T> FusedIterator for Drain<'_, T> {} |