Reinstate AsSlice impls for Option and Result

Author: Nick Cameron

src/libcore/option.rs

@@ -149,6 +149,7 @@ use iter::{Iterator, DoubleEndedIterator, FromIterator, ExactSize};
 use mem;
 use result::{Result, Ok, Err};
 use slice;
+use slice::AsSlice;
 
 // Note that this is not a lang item per se, but it has a hidden dependency on
 // `Iterator`, which is one. The compiler assumes that the `next` method of
@@ -845,6 +846,21 @@ impl<T: Default> Option<T> {
 // Trait implementations
 /////////////////////////////////////////////////////////////////////////////
 
+impl<T> AsSlice<T> for Option<T> {
+    /// Convert from `Option<T>` to `&[T]` (without copying)
+    #[inline]
+    #[stable]
+    fn as_slice<'a>(&'a self) -> &'a [T] {
+        match *self {
+            Some(ref x) => slice::ref_slice(x),
+            None => {
+                let result: &[_] = &[];
+                result
+            }
+        }
+    }
+}
+
 impl<T> Default for Option<T> {
     #[inline]
     fn default() -> Option<T> { None }

src/libcore/result.rs

@@ -280,6 +280,7 @@ use clone::Clone;
 use cmp::PartialEq;
 use std::fmt::Show;
 use slice;
+use slice::AsSlice;
 use iter::{Iterator, DoubleEndedIterator, FromIterator, ExactSize};
 use option::{None, Option, Some};
 
@@ -839,6 +840,26 @@ impl<T: Show, E> Result<T, E> {
     }
 }
 
+/////////////////////////////////////////////////////////////////////////////
+// Trait implementations
+/////////////////////////////////////////////////////////////////////////////
+
+impl<T, E> AsSlice<T> for Result<T, E> {
+    /// Convert from `Result<T, E>` to `&[T]` (without copying)
+    #[inline]
+    #[stable]
+    fn as_slice<'a>(&'a self) -> &'a [T] {
+        match *self {
+            Ok(ref x) => slice::ref_slice(x),
+            Err(_) => {
+                // work around lack of implicit coercion from fixed-size array to slice
+                let emp: &[_] = &[];
+                emp
+            }
+        }
+    }
+}
+
 /////////////////////////////////////////////////////////////////////////////
 // The Result Iterator
 /////////////////////////////////////////////////////////////////////////////