Add AsRef, as_slice, as_str to more things

.gitignore

@@ -42,7 +42,7 @@ __pycache__/
 /src/libcore/unicode/SpecialCasing.txt
 /src/libcore/unicode/UnicodeData.txt
 /src/libcore/unicode/downloaded
-/target/
+target/
 # Generated by compiletest for incremental:
 /tmp/
 tags

src/libcore/iter/adapters/mod.rs

@@ -1,8 +1,9 @@
 use crate::cmp;
 use crate::fmt;
+use crate::intrinsics;
 use crate::ops::{Add, AddAssign, Try};
+use crate::slice;
 use crate::usize;
-use crate::intrinsics;
 
 use super::{Iterator, DoubleEndedIterator, ExactSizeIterator, FusedIterator, TrustedLen};
 use super::{LoopState, from_fn};
@@ -234,6 +235,29 @@ unsafe impl<'a, I, T: 'a> TrustedLen for Copied<I>
           T: Copy
 {}
 
+#[stable(feature = "slice_iter_adapter_as_ref", since = "1.41.0")]
+impl<'a, T> AsRef<[T]> for Copied<slice::Iter<'a, T>> {
+    fn as_ref(&self) -> &[T] {
+        self.it.as_ref()
+    }
+}
+impl<'a, T> Copied<slice::Iter<'a, T>> {
+    /// This simply calls the parent method. For more information, see
+    /// [`Iter::as_slice`][slice::Iter::as_slice].
+    #[unstable(feature = "slice_iter_adapter_as_slice", issue = "0")]
+    pub fn as_slice(&self) -> &'a [T] {
+        self.it.as_slice()
+    }
+}
+impl<'a, T> Copied<slice::IterMut<'a, T>> {
+    /// This simply calls the parent method. For more information, see
+    /// [`IterMut::as_slice`][slice::IterMut::as_slice].
+    #[unstable(feature = "slice_iter_adapter_as_slice", issue = "0")]
+    pub fn as_slice(&self) -> &[T] {
+        self.it.as_slice()
+    }
+}
+
 /// An iterator that clones the elements of an underlying iterator.
 ///
 /// This `struct` is created by the [`cloned`] method on [`Iterator`]. See its
@@ -357,6 +381,29 @@ unsafe impl<'a, I, T: 'a> TrustedLen for Cloned<I>
           T: Clone
 {}
 
+#[stable(feature = "slice_iter_adapter_as_ref", since = "1.41.0")]
+impl<'a, T> AsRef<[T]> for Cloned<slice::Iter<'a, T>> {
+    fn as_ref(&self) -> &[T] {
+        self.it.as_ref()
+    }
+}
+impl<'a, T> Cloned<slice::Iter<'a, T>> {
+    /// This simply calls the parent method. For more information, see
+    /// [`Iter::as_slice`][slice::Iter::as_slice].
+    #[unstable(feature = "slice_iter_adapter_as_slice", issue = "0")]
+    pub fn as_slice(&self) -> &'a [T] {
+        self.it.as_slice()
+    }
+}
+impl<'a, T> Cloned<slice::IterMut<'a, T>> {
+    /// This simply calls the parent method. For more information, see
+    /// [`IterMut::as_slice`][slice::IterMut::as_slice].
+    #[unstable(feature = "slice_iter_adapter_as_slice", issue = "0")]
+    pub fn as_slice(&self) -> &[T] {
+        self.it.as_slice()
+    }
+}
+
 /// An iterator that repeats endlessly.
 ///
 /// This `struct` is created by the [`cycle`] method on [`Iterator`]. See its
@@ -1222,6 +1269,28 @@ unsafe impl<I> TrustedLen for Enumerate<I>
     where I: TrustedLen,
 {}
 
+#[stable(feature = "slice_iter_adapter_as_ref", since = "1.41.0")]
+impl<'a, T> AsRef<[T]> for Enumerate<slice::Iter<'a, T>> {
+    fn as_ref(&self) -> &[T] {
+        self.iter.as_ref()
+    }
+}
+impl<'a, T> Enumerate<slice::Iter<'a, T>> {
+    /// This simply calls the parent method. For more information, see
+    /// [`Iter::as_slice`][slice::Iter::as_slice].
+    #[unstable(feature = "slice_iter_adapter_as_slice", issue = "0")]
+    pub fn as_slice(&self) -> &'a [T] {
+        self.iter.as_slice()
+    }
+}
+impl<'a, T> Enumerate<slice::IterMut<'a, T>> {
+    /// This simply calls the parent method. For more information, see
+    /// [`IterMut::as_slice`][slice::IterMut::as_slice].
+    #[unstable(feature = "slice_iter_adapter_as_slice", issue = "0")]
+    pub fn as_slice(&self) -> &[T] {
+        self.iter.as_slice()
+    }
+}
 
 /// An iterator with a `peek()` that returns an optional reference to the next
 /// element.

src/libcore/str/mod.rs

@@ -651,6 +651,19 @@ impl<'a> Chars<'a> {
     }
 }
 
+#[stable(feature = "chars_as_ref", since = "1.41.0")]
+impl<'a> AsRef<str> for Chars<'a> {
+    fn as_ref(&self) -> &str {
+        self.as_str()
+    }
+}
+#[stable(feature = "chars_as_ref", since = "1.41.0")]
+impl<'a> AsRef<[u8]> for Chars<'a> {
+    fn as_ref(&self) -> &[u8] {
+        self.as_str().as_bytes()
+    }
+}
+
 /// An iterator over the [`char`]s of a string slice, and their positions.
 ///
 /// [`char`]: ../../std/primitive.char.html
@@ -728,6 +741,19 @@ impl<'a> CharIndices<'a> {
     }
 }
 
+#[stable(feature = "chars_as_ref", since = "1.41.0")]
+impl<'a> AsRef<str> for CharIndices<'a> {
+    fn as_ref(&self) -> &str {
+        self.as_str()
+    }
+}
+#[stable(feature = "chars_as_ref", since = "1.41.0")]
+impl<'a> AsRef<[u8]> for CharIndices<'a> {
+    fn as_ref(&self) -> &[u8] {
+        self.as_str().as_bytes()
+    }
+}
+
 /// An iterator over the bytes of a string slice.
 ///
 /// This struct is created by the [`bytes`] method on [`str`].
@@ -739,6 +765,18 @@ impl<'a> CharIndices<'a> {
 #[derive(Clone, Debug)]
 pub struct Bytes<'a>(Cloned<slice::Iter<'a, u8>>);
 
+impl<'a> Bytes<'a> {
+    /// Views the underlying data as a subslice of the original data.
+    ///
+    /// This has the same lifetime as the original slice, and so the
+    /// iterator can continue to be used while this exists.
+    #[unstable(feature = "bytes_as_bytes", issue = "0")]
+    #[inline]
+    pub fn as_bytes(&self) -> &'a [u8] {
+        self.0.as_slice()
+    }
+}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl Iterator for Bytes<'_> {
     type Item = u8;
@@ -847,6 +885,13 @@ unsafe impl TrustedRandomAccess for Bytes<'_> {
     fn may_have_side_effect() -> bool { false }
 }
 
+#[stable(feature = "bytes_as_ref", since = "1.41.0")]
+impl<'a> AsRef<[u8]> for Bytes<'a> {
+    fn as_ref(&self) -> &[u8] {
+        self.0.as_ref()
+    }
+}
+
 /// This macro generates a Clone impl for string pattern API
 /// wrapper types of the form X<'a, P>
 macro_rules! derive_pattern_clone {