Struct staticvec::StaticHeap

pub struct StaticHeap<T, const N: usize> { /* fields omitted */ }

A priority queue implemented as a binary heap, built around an instance of StaticVec<T, N>.

StaticHeap, as well as the associated iterator and helper structs for it are direct adaptations of the ones found in the std::collections::binary_heap module (including most of the documentation, at least for the functions that exist in both implementations).

It is a logic error for an item to be modified in such a way that the item's ordering relative to any other item, as determined by the Ord trait, changes while it is in the heap. This is normally only possible through Cell, RefCell, global state, I/O, or unsafe code.

Examples

use staticvec::StaticHeap;

let mut heap = StaticHeap::<i32, 4>::new();

// We can use peek to look at the next item in the heap. In this case,
// there's no items in there yet so we get None.
assert_eq!(heap.peek(), None);

// Let's add some scores...
heap.push(1);
heap.push(5);
heap.push(2);

// Now peek shows the most important item in the heap.
assert_eq!(heap.peek(), Some(&5));

// We can check the length of a heap.
assert_eq!(heap.len(), 3);

// We can iterate over the items in the heap, although they are returned in
// a random order.
for x in &heap {
  println!("{}", x);
}

// If we instead pop these scores, they should come back in order.
assert_eq!(heap.pop(), Some(5));
assert_eq!(heap.pop(), Some(2));
assert_eq!(heap.pop(), Some(1));
assert_eq!(heap.pop(), None);

// We can clear the heap of any remaining items.
heap.clear();

// The heap should now be empty.
assert!(heap.is_empty())

Min-heap

Either core::cmp::Reverse or a custom Ord implementation can be used to make StaticHeap a min-heap. This makes heap.pop() return the smallest value instead of the greatest one.

use staticvec::StaticHeap;
use core::cmp::Reverse;

// Wrap the values in `Reverse`.
let mut heap = StaticHeap::from([Reverse(1), Reverse(5), Reverse(2)]);

// If we pop these scores now, they should come back in the reverse order.
assert_eq!(heap.pop(), Some(Reverse(1)));
assert_eq!(heap.pop(), Some(Reverse(2)));
assert_eq!(heap.pop(), Some(Reverse(5)));
assert_eq!(heap.pop(), None);

Time complexity

push	pop	peek/peek_mut
O(1)~	O(log n)	O(1)

The value for push is an expected cost; the method documentation gives a more detailed analysis.

Methods

impl<T: Ord, const N: usize> StaticHeap<T, N>

pub const fn new() -> StaticHeap<T, N>

Creates an empty StaticHeap as a max-heap.

Examples

Basic usage:

let mut heap = StaticHeap::<i32, 2>::new();
heap.push(4);

pub const fn peek_mut(&mut self) -> Option<StaticHeapPeekMut<T, N>>

Returns a mutable reference to the greatest item in the StaticHeap, or None if it is empty.

Note: If the StaticHeapPeekMut value is leaked, the heap may be in an inconsistent state.

Examples

Basic usage:

let mut heap = StaticHeap::<i32, 4>::new();
assert!(heap.peek_mut().is_none());
heap.push(1);
heap.push(5);
heap.push(2);
{
  let mut val = heap.peek_mut().unwrap();
  *val = 0;
}
assert_eq!(heap.peek(), Some(&2));

Time complexity

Cost is O(1) in the worst case.

pub unsafe fn pop_unchecked(&mut self) -> T

Pops a value from the end of the StaticHeap and returns it directly without asserting that the StaticHeap's current length is greater than 0.

Safety

It is up to the caller to ensure that the StaticHeap contains at least one element prior to using this function. Failure to do so will result in reading from uninitialized memory.

Examples

Basic usage:

let mut heap = StaticHeap::from([1, 3]);
unsafe {
  assert_eq!(heap.pop_unchecked(), 3);
  assert_eq!(heap.pop_unchecked(), 1);
}

Time complexity

The worst case cost of pop_unchecked on a heap containing n elements is O(log n).

pub fn pop(&mut self) -> Option<T>

Removes the greatest item from the StaticHeap and returns it, or None if it is empty.

Examples

Basic usage:

let mut heap = StaticHeap::from([1, 3]);
assert_eq!(heap.pop(), Some(3));
assert_eq!(heap.pop(), Some(1));
assert_eq!(heap.pop(), None);

Time complexity

The worst case cost of pop on a heap containing n elements is O(log n).

pub unsafe fn push_unchecked(&mut self, item: T)

Pushes a value onto the StaticHeap without asserting that its current length is less than self.capacity().

Safety

It is up to the caller to ensure that the length of the StaticHeap prior to using this function is less than self.capacity(). Failure to do so will result in writing to an out-of-bounds memory region.

Examples

Basic usage:

let mut heap = StaticHeap::<i32, 3>::new();
unsafe {
  heap.push_unchecked(3);
  heap.push_unchecked(5);
  heap.push_unchecked(1);
}
assert_eq!(heap.len(), 3);
assert_eq!(heap.peek(), Some(&5));

Time complexity

The expected cost of push_unchecked, averaged over every possible ordering of the elements being pushed, and over a sufficiently large number of pushes, is O(1). This is the most meaningful cost metric when pushing elements that are not already in any sorted pattern.

The time complexity degrades if elements are pushed in predominantly ascending order. In the worst case, elements are pushed in ascending sorted order and the amortized cost per push is O(log n) against a heap containing n elements.

The worst case cost of a single call to push_unchecked is O(n).

pub fn push(&mut self, item: T)

Pushes an item onto the StaticHeap, panicking if the underlying StaticVec instance is already at maximum capacity.

Examples

Basic usage:

let mut heap = StaticHeap::<i32, 5>::new();
heap.push(3);
heap.push(5);
heap.push(1);
assert_eq!(heap.len(), 3);
assert_eq!(heap.peek(), Some(&5));

Time complexity

The expected cost of push, averaged over every possible ordering of the elements being pushed, and over a sufficiently large number of pushes, is O(1). This is the most meaningful cost metric when pushing elements that are not already in any sorted pattern.

The time complexity degrades if elements are pushed in predominantly ascending order. In the worst case, elements are pushed in ascending sorted order and the amortized cost per push is O(log n) against a heap containing n elements.

The worst case cost of a single call to push is O(n).

pub fn into_sorted_staticvec(self) -> StaticVec<T, N>

Consumes the StaticHeap and returns a StaticVec in sorted (ascending) order.

Examples

Basic usage:

let mut heap = StaticHeap::<i32, 8>::from([1, 2, 4, 5, 7]);
heap.push(6);
heap.push(3);
let vec = heap.into_sorted_staticvec();
assert_eq!(vec, [1, 2, 3, 4, 5, 6, 7]);

pub fn append<const N2: usize>(&mut self, other: &mut StaticHeap<T, N2>)

Appends self.remaining_capacity() (or as many as available) items from other to self. The appended items (if any) will no longer exist in other afterwards (which is to say, other will be left empty.)

The N2 parameter does not need to be provided explicitly, and can be inferred directly from the constant N2 constraint of other (which may or may not be the same as the N constraint of self.)

Examples

Basic usage:

// We give the two heaps arbitrary capacities for the sake of the example.
let mut a = StaticHeap::<i32, 9>::from([-10, 1, 2, 3, 3]);
let mut b = StaticHeap::<i32, 18>::from([-20, 5, 43]);
a.append(&mut b);
assert_eq!(a.into_sorted_staticvec(), [-20, -10, 1, 2, 3, 3, 5, 43]);
assert!(b.is_empty());

pub const fn drain_sorted(&mut self) -> StaticHeapDrainSorted<T, N>

Returns an iterator which retrieves elements in heap order. The retrieved elements are removed from the original heap. The remaining elements will be removed on drop in heap order.

Note:

• drain_sorted() is O(n log n); much slower than drain(). You should use the latter for most cases.

Examples

Basic usage:

let mut heap = StaticHeap::from([1, 2, 3, 4, 5]);
assert_eq!(heap.len(), 5);
drop(heap.drain_sorted()); // removes all elements in heap order
assert_eq!(heap.len(), 0);

impl<T, const N: usize> StaticHeap<T, N>

pub fn iter(&self) -> StaticVecIterConst<T, N>

Returns an iterator visiting all values in the StaticHeap's underlying StaticVec, in arbitrary order.

Examples

Basic usage:

let heap = StaticHeap::from(staticvec![1, 2, 3, 4]);
// Print 1, 2, 3, 4 in arbitrary order
for x in heap.iter() {
  println!("{}", x);
}

pub fn iter_mut(&mut self) -> StaticVecIterMut<T, N>

Returns a mutable iterator visiting all values in the StaticHeap's underlying StaticVec, in arbitrary order.

Note: Mutating the elements in a StaticHeap may cause it to become unbalanced.

Examples

Basic usage:

let mut heap = StaticHeap::from([1, 2, 3, 4]);
for i in heap.iter_mut() {
  *i *= 2;
}
// Prints "[2, 4, 6, 8]", but in arbitrary order
println!("{:?}", heap);

pub const fn into_iter_sorted(self) -> StaticHeapIntoIterSorted<T, N>

Returns an iterator which retrieves elements in heap order. This method consumes the original StaticHeap.

Examples

Basic usage:

let heap = StaticHeap::from([1, 2, 3, 4, 5]);
assert_eq!(
  heap.into_iter_sorted().take(2).collect::<StaticVec<_, 3>>(), staticvec![5, 4]
);

pub fn peek(&self) -> Option<&T>

Returns the greatest item in the StaticHeap, or None if it is empty.

Examples

Basic usage:

let mut heap = StaticHeap::<i32, 7>::new();
assert_eq!(heap.peek(), None);
heap.push(1);
heap.push(5);
heap.push(2);
assert_eq!(heap.peek(), Some(&5));

Time complexity

Cost is O(1) in the worst case.

pub const fn capacity(&self) -> usize

Returns the maximum number of elements the StaticHeap can hold. This is always equivalent to its constant generic N parameter.

Examples

Basic usage:

let mut heap = StaticHeap::<i32, 100>::new();
assert!(heap.capacity() >= 100);
heap.push(4);

pub const fn remaining_capacity(&self) -> usize

Returns the remaining capacity (which is to say, self.capacity() - self.len()) of the StaticHeap.

Examples

Basic usage:

let mut heap = StaticHeap::<i32, 100>::new();
heap.push(1);
assert_eq!(heap.remaining_capacity(), 99);

pub const fn size_in_bytes(&self) -> usize

Returns the total size of the inhabited part of the StaticHeap (which may be zero if it has a length of zero or contains ZSTs) in bytes. Specifically, the return value of this function amounts to a calculation of size_of::<T>() * self.length.

Examples

Basic usage:

let x = StaticHeap::<u8, 8>::from([1, 2, 3, 4, 5, 6, 7, 8]);
assert_eq!(x.size_in_bytes(), 8);
let y = StaticHeap::<u16, 8>::from([1, 2, 3, 4, 5, 6, 7, 8]);
assert_eq!(y.size_in_bytes(), 16);
let z = StaticHeap::<u32, 8>::from([1, 2, 3, 4, 5, 6, 7, 8]);
assert_eq!(z.size_in_bytes(), 32);
let w = StaticHeap::<u64, 8>::from([1, 2, 3, 4, 5, 6, 7, 8]);
assert_eq!(w.size_in_bytes(), 64);

pub fn into_staticvec(self) -> StaticVec<T, N>

Consumes the StaticHeap and returns the underlying StaticVec in arbitrary order.

Examples

Basic usage:

let heap = StaticHeap::from(staticvec![1, 2, 3, 4, 5, 6, 7]);
let vec = heap.into_staticvec();
// Will print in some order
for x in &vec {
  println!("{}", x);
}

pub const fn len(&self) -> usize

Returns the length of the StaticHeap.

Examples

Basic usage:

let heap = StaticHeap::from(staticvec![1, 3]);
assert_eq!(heap.len(), 2);

pub const fn is_empty(&self) -> bool

Returns true if the current length of the StaticHeap is 0.

Examples

Basic usage:

let mut heap = StaticHeap::<i32, 28>::new();
assert!(heap.is_empty());

pub const fn is_not_empty(&self) -> bool

Returns true if the current length of the StaticHeap is greater than 0.

Examples

Basic usage:

let mut heap = StaticHeap::<i32, 2>::new();
heap.push(1);
assert!(heap.is_not_empty());

pub const fn is_full(&self) -> bool

Returns true if the current length of the StaticHeap is equal to its capacity.

Examples

Basic usage:

let mut heap = StaticHeap::<i32, 4>::new();
heap.push(3);
heap.push(5);
heap.push(1);
heap.push(2);
assert!(heap.is_full());

pub const fn is_not_full(&self) -> bool

Returns true if the current length of the StaticHeap is less than its capacity.

Examples

Basic usage:

let mut heap = StaticHeap::<i32, 4>::new();
heap.push(3);
heap.push(5);
heap.push(1);
assert!(heap.is_not_full());

pub fn drain(&mut self) -> StaticVecDrain<T, N>

Clears the StaticHeap, returning an iterator over the removed elements.

The elements are removed in arbitrary order.

Examples

Basic usage:

let mut heap = StaticHeap::from(staticvec![1, 3]);
assert!(heap.is_not_empty());
for x in heap.drain() {
  println!("{}", x);
}
assert!(heap.is_empty());

pub fn clear(&mut self)

Drops all items from the StaticHeap.

Examples

Basic usage:

let mut heap = StaticHeap::from(staticvec![1, 3]);
assert!(heap.is_not_empty());
heap.clear();
assert!(heap.is_empty());

Trait Implementations

impl<T: Clone, const N: usize> Clone for StaticHeap<T, N>

default fn clone(&self) -> Self

Returns a copy of the value.

default fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<T: Copy, const N: usize> Clone for StaticHeap<T, N>

fn clone(&self) -> Self

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<T: Debug, const N: usize> Debug for StaticHeap<T, N>

fn fmt(&self, f: &mut Formatter) -> Result

Formats the value using the given formatter.

impl<T: Ord, const N: usize> Default for StaticHeap<T, N>

fn default() -> StaticHeap<T, N>

Creates an empty StaticHeap<T, N>.

impl<'a, T: 'a + Copy + Ord, const N: usize> Extend<&'a T> for StaticHeap<T, N>

fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I)

Extends a collection with the contents of an iterator.

impl<T: Ord, const N: usize> Extend<T> for StaticHeap<T, N>

fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I)

Extends a collection with the contents of an iterator.

impl<T: Ord, const N: usize> From<[T; N]> for StaticHeap<T, N>

fn from(array: [T; N]) -> StaticHeap<T, N>

Converts a [T; N] into a StaticHeap<T, N>. This conversion happens in-place, and has O(n) time complexity.

impl<T: Ord, const N1: usize, const N2: usize> From<[T; N1]> for StaticHeap<T, N2>

default fn from(array: [T; N1]) -> StaticHeap<T, N2>

Converts a [T; N1] into a StaticHeap<T, N2>. This conversion happens in-place, and has O(n) time complexity.

impl<T, const N: usize> From<StaticHeap<T, N>> for StaticVec<T, N>

fn from(heap: StaticHeap<T, N>) -> StaticVec<T, N>

Performs the conversion.

impl<T, const N1: usize, const N2: usize> From<StaticHeap<T, N1>> for StaticVec<T, N2>

default fn from(heap: StaticHeap<T, N1>) -> StaticVec<T, N2>

Performs the conversion.

impl<T: Ord, const N: usize> From<StaticVec<T, N>> for StaticHeap<T, N>

fn from(vec: StaticVec<T, N>) -> StaticHeap<T, N>

Converts a StaticVec<T, N> into a StaticHeap<T, N>. This conversion happens in-place, and has O(n) time complexity.

impl<T: Ord, const N1: usize, const N2: usize> From<StaticVec<T, N1>> for StaticHeap<T, N2>

default fn from(vec: StaticVec<T, N1>) -> StaticHeap<T, N2>

Converts a StaticVec<T, N1> into a StaticHeap<T, N2>. This conversion happens in-place, and has O(n) time complexity.

impl<'a, T: 'a + Copy + Ord, const N: usize> FromIterator<&'a T> for StaticHeap<T, N>

fn from_iter<I: IntoIterator<Item = &'a T>>(iter: I) -> StaticHeap<T, N>

Creates a value from an iterator.

impl<T: Ord, const N: usize> FromIterator<T> for StaticHeap<T, N>

fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> StaticHeap<T, N>

Creates a value from an iterator.

impl<T, const N: usize> IntoIterator for StaticHeap<T, N>

type Item = T

The type of the elements being iterated over.

type IntoIter = StaticVecIntoIter<T, N>

Which kind of iterator are we turning this into?

fn into_iter(self) -> StaticVecIntoIter<T, N>

Creates a consuming iterator, that is, one that moves each value out of the binary heap in arbitrary order. The binary heap cannot be used after calling this.

Examples

Basic usage:

let heap = StaticHeap::from([1, 2, 3, 4]);
// Print 1, 2, 3, 4 in arbitrary order
for x in heap.into_iter() {
  // x has type i32, not &i32
  println!("{}", x);
}

impl<'a, T, const N: usize> IntoIterator for &'a StaticHeap<T, N>

type Item = &'a T

The type of the elements being iterated over.

type IntoIter = StaticVecIterConst<'a, T, N>

Which kind of iterator are we turning this into?

fn into_iter(self) -> StaticVecIterConst<'a, T, N>

Creates an iterator from a value.

impl<'a, T, const N: usize> IntoIterator for &'a mut StaticHeap<T, N>

type Item = &'a mut T

The type of the elements being iterated over.

type IntoIter = StaticVecIterMut<'a, T, N>

Which kind of iterator are we turning this into?

fn into_iter(self) -> StaticVecIterMut<'a, T, N>

Creates an iterator from a value.