collections: Add trait RangeArgument

RangeArgument is introduced as unstable under the
feature(collections_range)

src/libcollections/lib.rs

@@ -82,6 +82,7 @@
 pub mod enum_set;
 pub mod fmt;
 pub mod linked_list;
+pub mod range;
 pub mod slice;
 pub mod str;
 pub mod string;

src/libcollections/range.rs

+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+#![unstable(feature = "collections_range", reason = "was just added")]
+
+//! Range syntax.
+
+use core::option::Option::{self, None, Some};
+use core::ops::{RangeFull, Range, RangeTo, RangeFrom};
+
+/// **RangeArgument** is implemented by Rust's built-in range types, produced
+/// by range syntax like `..`, `a..`, `..b` or `c..d`.
+pub trait RangeArgument<T> {
+    /// Start index (inclusive)
+    ///
+    /// Return start value if present, else `None`.
+    fn start(&self) -> Option<&T> { None }
+
+    /// End index (exclusive)
+    ///
+    /// Return end value if present, else `None`.
+    fn end(&self) -> Option<&T> { None }
+}
+
+
+impl<T> RangeArgument<T> for RangeFull {}
+
+impl<T> RangeArgument<T> for RangeFrom<T> {
+    fn start(&self) -> Option<&T> { Some(&self.start) }
+}
+
+impl<T> RangeArgument<T> for RangeTo<T> {
+    fn end(&self) -> Option<&T> { Some(&self.end) }
+}
+
+impl<T> RangeArgument<T> for Range<T> {
+    fn start(&self) -> Option<&T> { Some(&self.start) }
+    fn end(&self) -> Option<&T> { Some(&self.end) }
+}