2 use crate::iter::{FusedIterator, TrustedLen};
5 /// Creates an iterator that yields nothing.
14 /// // this could have been an iterator over i32, but alas, it's just not.
15 /// let mut nope = iter::empty::<i32>();
17 /// assert_eq!(None, nope.next());
19 #[stable(feature = "iter_empty", since = "1.2.0")]
20 #[rustc_const_stable(feature = "const_iter_empty", since = "1.32.0")]
21 pub const fn empty<T>() -> Empty<T> {
22 Empty(marker::PhantomData)
25 /// An iterator that yields nothing.
27 /// This `struct` is created by the [`empty()`] function. See its documentation for more.
28 #[must_use = "iterators are lazy and do nothing unless consumed"]
29 #[stable(feature = "iter_empty", since = "1.2.0")]
30 pub struct Empty<T>(marker::PhantomData<fn() -> T>);
32 #[stable(feature = "core_impl_debug", since = "1.9.0")]
33 impl<T> fmt::Debug for Empty<T> {
34 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
35 f.debug_struct("Empty").finish()
39 #[stable(feature = "iter_empty", since = "1.2.0")]
40 impl<T> Iterator for Empty<T> {
43 fn next(&mut self) -> Option<T> {
47 fn size_hint(&self) -> (usize, Option<usize>) {
52 #[stable(feature = "iter_empty", since = "1.2.0")]
53 impl<T> DoubleEndedIterator for Empty<T> {
54 fn next_back(&mut self) -> Option<T> {
59 #[stable(feature = "iter_empty", since = "1.2.0")]
60 impl<T> ExactSizeIterator for Empty<T> {
61 fn len(&self) -> usize {
66 #[unstable(feature = "trusted_len", issue = "37572")]
67 unsafe impl<T> TrustedLen for Empty<T> {}
69 #[stable(feature = "fused", since = "1.26.0")]
70 impl<T> FusedIterator for Empty<T> {}
72 // not #[derive] because that adds a Clone bound on T,
73 // which isn't necessary.
74 #[stable(feature = "iter_empty", since = "1.2.0")]
75 impl<T> Clone for Empty<T> {
76 fn clone(&self) -> Empty<T> {
77 Empty(marker::PhantomData)
81 // not #[derive] because that adds a Default bound on T,
82 // which isn't necessary.
83 #[stable(feature = "iter_empty", since = "1.2.0")]
84 #[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
85 impl<T> const Default for Empty<T> {
86 fn default() -> Empty<T> {
87 Empty(marker::PhantomData)