1 // Copyright 2013-2016 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
15 use option::Option::{self, Some, None};
18 use super::{DoubleEndedIterator, IntoIterator, Iterator, ExactSizeIterator};
20 /// An iterator that repeats an element endlessly.
22 /// This `struct` is created by the [`repeat()`] function. See its documentation for more.
24 /// [`repeat()`]: fn.repeat.html
25 #[derive(Clone, Debug)]
26 #[stable(feature = "rust1", since = "1.0.0")]
27 pub struct Repeat<A> {
31 #[stable(feature = "rust1", since = "1.0.0")]
32 impl<A: Clone> Iterator for Repeat<A> {
36 fn next(&mut self) -> Option<A> { Some(self.element.clone()) }
38 fn size_hint(&self) -> (usize, Option<usize>) { (usize::MAX, None) }
41 #[stable(feature = "rust1", since = "1.0.0")]
42 impl<A: Clone> DoubleEndedIterator for Repeat<A> {
44 fn next_back(&mut self) -> Option<A> { Some(self.element.clone()) }
47 /// Creates a new iterator that endlessly repeats a single element.
49 /// The `repeat()` function repeats a single value over and over and over and
50 /// over and over and 🔁.
52 /// Infinite iterators like `repeat()` are often used with adapters like
53 /// [`take()`], in order to make them finite.
55 /// [`take()`]: trait.Iterator.html#method.take
64 /// // the number four 4ever:
65 /// let mut fours = iter::repeat(4);
67 /// assert_eq!(Some(4), fours.next());
68 /// assert_eq!(Some(4), fours.next());
69 /// assert_eq!(Some(4), fours.next());
70 /// assert_eq!(Some(4), fours.next());
71 /// assert_eq!(Some(4), fours.next());
73 /// // yup, still four
74 /// assert_eq!(Some(4), fours.next());
77 /// Going finite with [`take()`]:
82 /// // that last example was too many fours. Let's only have four fours.
83 /// let mut four_fours = iter::repeat(4).take(4);
85 /// assert_eq!(Some(4), four_fours.next());
86 /// assert_eq!(Some(4), four_fours.next());
87 /// assert_eq!(Some(4), four_fours.next());
88 /// assert_eq!(Some(4), four_fours.next());
90 /// // ... and now we're done
91 /// assert_eq!(None, four_fours.next());
94 #[stable(feature = "rust1", since = "1.0.0")]
95 pub fn repeat<T: Clone>(elt: T) -> Repeat<T> {
99 /// An iterator that yields nothing.
101 /// This `struct` is created by the [`empty()`] function. See its documentation for more.
103 /// [`empty()`]: fn.empty.html
104 #[stable(feature = "iter_empty", since = "1.2.0")]
105 pub struct Empty<T>(marker::PhantomData<T>);
107 #[stable(feature = "core_impl_debug", since = "1.9.0")]
108 impl<T> fmt::Debug for Empty<T> {
109 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
114 #[stable(feature = "iter_empty", since = "1.2.0")]
115 impl<T> Iterator for Empty<T> {
118 fn next(&mut self) -> Option<T> {
122 fn size_hint(&self) -> (usize, Option<usize>){
127 #[stable(feature = "iter_empty", since = "1.2.0")]
128 impl<T> DoubleEndedIterator for Empty<T> {
129 fn next_back(&mut self) -> Option<T> {
134 #[stable(feature = "iter_empty", since = "1.2.0")]
135 impl<T> ExactSizeIterator for Empty<T> {
136 fn len(&self) -> usize {
141 // not #[derive] because that adds a Clone bound on T,
142 // which isn't necessary.
143 #[stable(feature = "iter_empty", since = "1.2.0")]
144 impl<T> Clone for Empty<T> {
145 fn clone(&self) -> Empty<T> {
146 Empty(marker::PhantomData)
150 // not #[derive] because that adds a Default bound on T,
151 // which isn't necessary.
152 #[stable(feature = "iter_empty", since = "1.2.0")]
153 impl<T> Default for Empty<T> {
154 fn default() -> Empty<T> {
155 Empty(marker::PhantomData)
159 /// Creates an iterator that yields nothing.
168 /// // this could have been an iterator over i32, but alas, it's just not.
169 /// let mut nope = iter::empty::<i32>();
171 /// assert_eq!(None, nope.next());
173 #[stable(feature = "iter_empty", since = "1.2.0")]
174 pub fn empty<T>() -> Empty<T> {
175 Empty(marker::PhantomData)
178 /// An iterator that yields an element exactly once.
180 /// This `struct` is created by the [`once()`] function. See its documentation for more.
182 /// [`once()`]: fn.once.html
183 #[derive(Clone, Debug)]
184 #[stable(feature = "iter_once", since = "1.2.0")]
186 inner: ::option::IntoIter<T>
189 #[stable(feature = "iter_once", since = "1.2.0")]
190 impl<T> Iterator for Once<T> {
193 fn next(&mut self) -> Option<T> {
197 fn size_hint(&self) -> (usize, Option<usize>) {
198 self.inner.size_hint()
202 #[stable(feature = "iter_once", since = "1.2.0")]
203 impl<T> DoubleEndedIterator for Once<T> {
204 fn next_back(&mut self) -> Option<T> {
205 self.inner.next_back()
209 #[stable(feature = "iter_once", since = "1.2.0")]
210 impl<T> ExactSizeIterator for Once<T> {
211 fn len(&self) -> usize {
216 /// Creates an iterator that yields an element exactly once.
218 /// This is commonly used to adapt a single value into a [`chain()`] of other
219 /// kinds of iteration. Maybe you have an iterator that covers almost
220 /// everything, but you need an extra special case. Maybe you have a function
221 /// which works on iterators, but you only need to process one value.
223 /// [`chain()`]: trait.Iterator.html#method.chain
232 /// // one is the loneliest number
233 /// let mut one = iter::once(1);
235 /// assert_eq!(Some(1), one.next());
237 /// // just one, that's all we get
238 /// assert_eq!(None, one.next());
241 /// Chaining together with another iterator. Let's say that we want to iterate
242 /// over each file of the `.foo` directory, but also a configuration file,
248 /// use std::path::PathBuf;
250 /// let dirs = fs::read_dir(".foo").unwrap();
252 /// // we need to convert from an iterator of DirEntry-s to an iterator of
253 /// // PathBufs, so we use map
254 /// let dirs = dirs.map(|file| file.unwrap().path());
256 /// // now, our iterator just for our config file
257 /// let config = iter::once(PathBuf::from(".foorc"));
259 /// // chain the two iterators together into one big iterator
260 /// let files = dirs.chain(config);
262 /// // this will give us all of the files in .foo as well as .foorc
264 /// println!("{:?}", f);
267 #[stable(feature = "iter_once", since = "1.2.0")]
268 pub fn once<T>(value: T) -> Once<T> {
269 Once { inner: Some(value).into_iter() }