/
sources.rs
549 lines (500 loc) · 15.4 KB
/
sources.rs
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// Copyright 2013-2016 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
use fmt;
use marker;
use usize;
use super::{FusedIterator, TrustedLen};
/// An iterator that repeats an element endlessly.
///
/// This `struct` is created by the [`repeat`] function. See its documentation for more.
///
/// [`repeat`]: fn.repeat.html
#[derive(Clone, Debug)]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Repeat<A> {
element: A
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<A: Clone> Iterator for Repeat<A> {
type Item = A;
#[inline]
fn next(&mut self) -> Option<A> { Some(self.element.clone()) }
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) { (usize::MAX, None) }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<A: Clone> DoubleEndedIterator for Repeat<A> {
#[inline]
fn next_back(&mut self) -> Option<A> { Some(self.element.clone()) }
}
#[stable(feature = "fused", since = "1.26.0")]
impl<A: Clone> FusedIterator for Repeat<A> {}
#[unstable(feature = "trusted_len", issue = "37572")]
unsafe impl<A: Clone> TrustedLen for Repeat<A> {}
/// Creates a new iterator that endlessly repeats a single element.
///
/// The `repeat()` function repeats a single value over and over and over and
/// over and over and 🔁.
///
/// Infinite iterators like `repeat()` are often used with adapters like
/// [`take`], in order to make them finite.
///
/// [`take`]: trait.Iterator.html#method.take
///
/// If the element type of the iterator you need does not implement `Clone`,
/// or if you do not want to keep the repeated element in memory, you can
/// instead use the [`repeat_with`] function.
///
/// [`repeat_with`]: fn.repeat_with.html
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::iter;
///
/// // the number four 4ever:
/// let mut fours = iter::repeat(4);
///
/// assert_eq!(Some(4), fours.next());
/// assert_eq!(Some(4), fours.next());
/// assert_eq!(Some(4), fours.next());
/// assert_eq!(Some(4), fours.next());
/// assert_eq!(Some(4), fours.next());
///
/// // yup, still four
/// assert_eq!(Some(4), fours.next());
/// ```
///
/// Going finite with [`take`]:
///
/// ```
/// use std::iter;
///
/// // that last example was too many fours. Let's only have four fours.
/// let mut four_fours = iter::repeat(4).take(4);
///
/// assert_eq!(Some(4), four_fours.next());
/// assert_eq!(Some(4), four_fours.next());
/// assert_eq!(Some(4), four_fours.next());
/// assert_eq!(Some(4), four_fours.next());
///
/// // ... and now we're done
/// assert_eq!(None, four_fours.next());
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn repeat<T: Clone>(elt: T) -> Repeat<T> {
Repeat{element: elt}
}
/// An iterator that repeats elements of type `A` endlessly by
/// applying the provided closure `F: FnMut() -> A`.
///
/// This `struct` is created by the [`repeat_with`] function.
/// See its documentation for more.
///
/// [`repeat_with`]: fn.repeat_with.html
#[derive(Copy, Clone, Debug)]
#[stable(feature = "iterator_repeat_with", since = "1.28.0")]
pub struct RepeatWith<F> {
repeater: F
}
#[stable(feature = "iterator_repeat_with", since = "1.28.0")]
impl<A, F: FnMut() -> A> Iterator for RepeatWith<F> {
type Item = A;
#[inline]
fn next(&mut self) -> Option<A> { Some((self.repeater)()) }
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) { (usize::MAX, None) }
}
#[stable(feature = "iterator_repeat_with", since = "1.28.0")]
impl<A, F: FnMut() -> A> FusedIterator for RepeatWith<F> {}
#[unstable(feature = "trusted_len", issue = "37572")]
unsafe impl<A, F: FnMut() -> A> TrustedLen for RepeatWith<F> {}
/// Creates a new iterator that repeats elements of type `A` endlessly by
/// applying the provided closure, the repeater, `F: FnMut() -> A`.
///
/// The `repeat_with()` function calls the repeater over and over and over and
/// over and over and 🔁.
///
/// Infinite iterators like `repeat_with()` are often used with adapters like
/// [`take`], in order to make them finite.
///
/// [`take`]: trait.Iterator.html#method.take
///
/// If the element type of the iterator you need implements `Clone`, and
/// it is OK to keep the source element in memory, you should instead use
/// the [`repeat`] function.
///
/// [`repeat`]: fn.repeat.html
///
/// An iterator produced by `repeat_with()` is not a `DoubleEndedIterator`.
/// If you need `repeat_with()` to return a `DoubleEndedIterator`,
/// please open a GitHub issue explaining your use case.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::iter;
///
/// // let's assume we have some value of a type that is not `Clone`
/// // or which don't want to have in memory just yet because it is expensive:
/// #[derive(PartialEq, Debug)]
/// struct Expensive;
///
/// // a particular value forever:
/// let mut things = iter::repeat_with(|| Expensive);
///
/// assert_eq!(Some(Expensive), things.next());
/// assert_eq!(Some(Expensive), things.next());
/// assert_eq!(Some(Expensive), things.next());
/// assert_eq!(Some(Expensive), things.next());
/// assert_eq!(Some(Expensive), things.next());
/// ```
///
/// Using mutation and going finite:
///
/// ```rust
/// use std::iter;
///
/// // From the zeroth to the third power of two:
/// let mut curr = 1;
/// let mut pow2 = iter::repeat_with(|| { let tmp = curr; curr *= 2; tmp })
/// .take(4);
///
/// assert_eq!(Some(1), pow2.next());
/// assert_eq!(Some(2), pow2.next());
/// assert_eq!(Some(4), pow2.next());
/// assert_eq!(Some(8), pow2.next());
///
/// // ... and now we're done
/// assert_eq!(None, pow2.next());
/// ```
#[inline]
#[stable(feature = "iterator_repeat_with", since = "1.28.0")]
pub fn repeat_with<A, F: FnMut() -> A>(repeater: F) -> RepeatWith<F> {
RepeatWith { repeater }
}
/// An iterator that yields nothing.
///
/// This `struct` is created by the [`empty`] function. See its documentation for more.
///
/// [`empty`]: fn.empty.html
#[stable(feature = "iter_empty", since = "1.2.0")]
pub struct Empty<T>(marker::PhantomData<T>);
#[stable(feature = "core_impl_debug", since = "1.9.0")]
impl<T> fmt::Debug for Empty<T> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
f.pad("Empty")
}
}
#[stable(feature = "iter_empty", since = "1.2.0")]
impl<T> Iterator for Empty<T> {
type Item = T;
fn next(&mut self) -> Option<T> {
None
}
fn size_hint(&self) -> (usize, Option<usize>){
(0, Some(0))
}
}
#[stable(feature = "iter_empty", since = "1.2.0")]
impl<T> DoubleEndedIterator for Empty<T> {
fn next_back(&mut self) -> Option<T> {
None
}
}
#[stable(feature = "iter_empty", since = "1.2.0")]
impl<T> ExactSizeIterator for Empty<T> {
fn len(&self) -> usize {
0
}
}
#[unstable(feature = "trusted_len", issue = "37572")]
unsafe impl<T> TrustedLen for Empty<T> {}
#[stable(feature = "fused", since = "1.26.0")]
impl<T> FusedIterator for Empty<T> {}
// not #[derive] because that adds a Clone bound on T,
// which isn't necessary.
#[stable(feature = "iter_empty", since = "1.2.0")]
impl<T> Clone for Empty<T> {
fn clone(&self) -> Empty<T> {
Empty(marker::PhantomData)
}
}
// not #[derive] because that adds a Default bound on T,
// which isn't necessary.
#[stable(feature = "iter_empty", since = "1.2.0")]
impl<T> Default for Empty<T> {
fn default() -> Empty<T> {
Empty(marker::PhantomData)
}
}
/// Creates an iterator that yields nothing.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::iter;
///
/// // this could have been an iterator over i32, but alas, it's just not.
/// let mut nope = iter::empty::<i32>();
///
/// assert_eq!(None, nope.next());
/// ```
#[stable(feature = "iter_empty", since = "1.2.0")]
pub const fn empty<T>() -> Empty<T> {
Empty(marker::PhantomData)
}
/// An iterator that yields an element exactly once.
///
/// This `struct` is created by the [`once`] function. See its documentation for more.
///
/// [`once`]: fn.once.html
#[derive(Clone, Debug)]
#[stable(feature = "iter_once", since = "1.2.0")]
pub struct Once<T> {
inner: ::option::IntoIter<T>
}
#[stable(feature = "iter_once", since = "1.2.0")]
impl<T> Iterator for Once<T> {
type Item = T;
fn next(&mut self) -> Option<T> {
self.inner.next()
}
fn size_hint(&self) -> (usize, Option<usize>) {
self.inner.size_hint()
}
}
#[stable(feature = "iter_once", since = "1.2.0")]
impl<T> DoubleEndedIterator for Once<T> {
fn next_back(&mut self) -> Option<T> {
self.inner.next_back()
}
}
#[stable(feature = "iter_once", since = "1.2.0")]
impl<T> ExactSizeIterator for Once<T> {
fn len(&self) -> usize {
self.inner.len()
}
}
#[unstable(feature = "trusted_len", issue = "37572")]
unsafe impl<T> TrustedLen for Once<T> {}
#[stable(feature = "fused", since = "1.26.0")]
impl<T> FusedIterator for Once<T> {}
/// Creates an iterator that yields an element exactly once.
///
/// This is commonly used to adapt a single value into a [`chain`] of other
/// kinds of iteration. Maybe you have an iterator that covers almost
/// everything, but you need an extra special case. Maybe you have a function
/// which works on iterators, but you only need to process one value.
///
/// [`chain`]: trait.Iterator.html#method.chain
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::iter;
///
/// // one is the loneliest number
/// let mut one = iter::once(1);
///
/// assert_eq!(Some(1), one.next());
///
/// // just one, that's all we get
/// assert_eq!(None, one.next());
/// ```
///
/// Chaining together with another iterator. Let's say that we want to iterate
/// over each file of the `.foo` directory, but also a configuration file,
/// `.foorc`:
///
/// ```no_run
/// use std::iter;
/// use std::fs;
/// use std::path::PathBuf;
///
/// let dirs = fs::read_dir(".foo").unwrap();
///
/// // we need to convert from an iterator of DirEntry-s to an iterator of
/// // PathBufs, so we use map
/// let dirs = dirs.map(|file| file.unwrap().path());
///
/// // now, our iterator just for our config file
/// let config = iter::once(PathBuf::from(".foorc"));
///
/// // chain the two iterators together into one big iterator
/// let files = dirs.chain(config);
///
/// // this will give us all of the files in .foo as well as .foorc
/// for f in files {
/// println!("{:?}", f);
/// }
/// ```
#[stable(feature = "iter_once", since = "1.2.0")]
pub fn once<T>(value: T) -> Once<T> {
Once { inner: Some(value).into_iter() }
}
/// Creates a new iterator where each iteration calls the provided closure
/// `F: FnMut(&mut St) -> Option<T>`.
///
/// This allows creating a custom iterator with any behavior
/// without using the more verbose syntax of creating a dedicated type
/// and implementing the `Iterator` trait for it.
///
/// In addition to its captures and environment,
/// the closure is given a mutable reference to some state
/// that is preserved across iterations.
/// That state starts as the given `initial_state` value.
///
/// Note that the `Unfold` iterator doesn’t make assumptions about the behavior of the closure,
/// and therefore conservatively does not implement [`FusedIterator`],
/// or override [`Iterator::size_hint`] from its default `(0, None)`.
///
/// [`FusedIterator`]: trait.FusedIterator.html
/// [`Iterator::size_hint`]: trait.Iterator.html#method.size_hint
///
/// # Examples
///
/// Let’s re-implement the counter iterator from [module-level documentation]:
///
/// [module-level documentation]: index.html
///
/// ```
/// #![feature(iter_unfold)]
/// let counter = std::iter::unfold(0, |count| {
/// // increment our count. This is why we started at zero.
/// *count += 1;
///
/// // check to see if we've finished counting or not.
/// if *count < 6 {
/// Some(*count)
/// } else {
/// None
/// }
/// });
/// assert_eq!(counter.collect::<Vec<_>>(), &[1, 2, 3, 4, 5]);
/// ```
#[inline]
#[unstable(feature = "iter_unfold", issue = /* FIXME */ "0")]
pub fn unfold<St, T, F>(initial_state: St, f: F) -> Unfold<St, F>
where F: FnMut(&mut St) -> Option<T>
{
Unfold {
state: initial_state,
f,
}
}
/// An iterator where each iteration calls the provided closure `F: FnMut(&mut St) -> Option<T>`.
///
/// This `struct` is created by the [`unfold`] function.
/// See its documentation for more.
///
/// [`unfold`]: fn.unfold.html
#[derive(Clone)]
#[unstable(feature = "iter_unfold", issue = /* FIXME */ "0")]
pub struct Unfold<St, F> {
state: St,
f: F,
}
#[unstable(feature = "iter_unfold", issue = /* FIXME */ "0")]
impl<St, T, F> Iterator for Unfold<St, F>
where F: FnMut(&mut St) -> Option<T>
{
type Item = T;
#[inline]
fn next(&mut self) -> Option<Self::Item> {
(self.f)(&mut self.state)
}
}
#[unstable(feature = "iter_unfold", issue = /* FIXME */ "0")]
impl<St: fmt::Debug, F> fmt::Debug for Unfold<St, F> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
f.debug_struct("Unfold")
.field("state", &self.state)
.finish()
}
}
/// Creates a new iterator where each successive item is computed based on the preceding one.
///
/// The iterator starts with the given first item (if any)
/// and calls the given `FnMut(&T) -> Option<T>` closure to compute each item’s successor.
///
/// ```
/// #![feature(iter_unfold)]
/// use std::iter::successors;
///
/// let powers_of_10 = successors(Some(1_u16), |n| n.checked_mul(10));
/// assert_eq!(powers_of_10.collect::<Vec<_>>(), &[1, 10, 100, 1_000, 10_000]);
/// ```
#[unstable(feature = "iter_unfold", issue = /* FIXME */ "0")]
pub fn successors<T, F>(first: Option<T>, succ: F) -> Successors<T, F>
where F: FnMut(&T) -> Option<T>
{
// If this function returned `impl Iterator<Item=T>`
// it could be based on `unfold` and not need a dedicated type.
// However having a named `Successors<T, F>` type allows it to be `Clone` when `T` and `F` are.
Successors {
next: first,
succ,
}
}
/// An new iterator where each successive item is computed based on the preceding one.
///
/// This `struct` is created by the [`successors`] function.
/// See its documentation for more.
///
/// [`successors`]: fn.successors.html
#[derive(Clone)]
#[unstable(feature = "iter_unfold", issue = /* FIXME */ "0")]
pub struct Successors<T, F> {
next: Option<T>,
succ: F,
}
#[unstable(feature = "iter_unfold", issue = /* FIXME */ "0")]
impl<T, F> Iterator for Successors<T, F>
where F: FnMut(&T) -> Option<T>
{
type Item = T;
#[inline]
fn next(&mut self) -> Option<Self::Item> {
self.next.take().map(|item| {
self.next = (self.succ)(&item);
item
})
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
if self.next.is_some() {
(1, None)
} else {
(0, Some(0))
}
}
}
#[unstable(feature = "iter_unfold", issue = /* FIXME */ "0")]
impl<T, F> FusedIterator for Successors<T, F>
where F: FnMut(&T) -> Option<T>
{}
#[unstable(feature = "iter_unfold", issue = /* FIXME */ "0")]
impl<T: fmt::Debug, F> fmt::Debug for Successors<T, F> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
f.debug_struct("Successors")
.field("next", &self.next)
.finish()
}
}