add str::get_unchecked(_mut) in accordance with slice

src/libcollections/str.rs

@@ -32,7 +32,7 @@ use borrow::{Borrow, ToOwned};
 use string::String;
 use std_unicode;
 use vec::Vec;
-use slice::SliceConcatExt;
+use slice::{SliceConcatExt, SliceIndex};
 use boxed::Box;
 
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -1815,4 +1815,20 @@ impl str {
         s.extend((0..n).map(|_| self));
         s
     }
+
+    #[unstable(feature = "str_range_slice", issue = "39932")]
+    pub fn get<I>(&self, index: I) -> Option<&I::Output>
+        where I: SliceIndex<u8>
+    {
+        let bytes : &[u8] = unsafe { mem::transmute(self) };
+        index.get(bytes)
+    }
+
+    #[unstable(feature = "str_range_slice", issue = "39932")]
+    pub fn get_mut<I>(&mut self, index: I) -> Option<&mut I::Output>
+        where I: SliceIndex<u8>
+    {
+        let bytes : &mut [u8] = unsafe { mem::transmute(self) };
+        index.get_mut(bytes)
+    }
 }

src/libcore/str/mod.rs

@@ -21,7 +21,7 @@ use char;
 use fmt;
 use iter::{Map, Cloned, FusedIterator};
 use mem;
-use slice;
+use slice::{self, SliceIndex};
 
 pub mod pattern;
 
@@ -1712,6 +1712,12 @@ pub trait StrExt {
     unsafe fn slice_unchecked(&self, begin: usize, end: usize) -> &str;
     #[stable(feature = "core", since = "1.6.0")]
     unsafe fn slice_mut_unchecked(&mut self, begin: usize, end: usize) -> &mut str;
+    #[unstable(feature = "str_range_slice", issue = "39932")]
+    unsafe fn get_unchecked<I>(&self, index: I) -> &I::Output
+        where I: SliceIndex<u8>;
+    #[unstable(feature = "str_range_slice", issue = "39932")]
+    unsafe fn get_unchecked_mut<I>(&mut self, index: I) -> &mut I::Output
+        where I: SliceIndex<u8>;
     #[stable(feature = "core", since = "1.6.0")]
     fn starts_with<'a, P: Pattern<'a>>(&'a self, pat: P) -> bool;
     #[stable(feature = "core", since = "1.6.0")]
@@ -2046,6 +2052,22 @@ impl StrExt for str {
 
     #[inline]
     fn parse<T: FromStr>(&self) -> Result<T, T::Err> { FromStr::from_str(self) }
+
+    #[inline]
+    unsafe fn get_unchecked<I>(&self, index: I) -> &I::Output
+        where I: SliceIndex<u8>
+    {
+        let bytes : &[u8] = mem::transmute(self);
+        index.get_unchecked(bytes)
+    }
+
+    #[inline]
+    unsafe fn get_unchecked_mut<I>(&mut self, index: I) -> &mut I::Output
+        where I: SliceIndex<u8>
+    {
+        let bytes : &mut [u8] = mem::transmute(self);
+        index.get_unchecked_mut(bytes)
+    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]