Implement conversion traits for primitive integer types

1 files changed, 43 insertions, 0 deletions

diff --git a/src/libcore/num/mod.rs b/src/libcore/num/mod.rs
index 340028b4beb..0b7dc216d41 100644
--- a/src/libcore/num/mod.rs
+++ b/src/libcore/num/mod.rs
@@ -17,6 +17,7 @@ use self::wrapping::OverflowingOps;
 
 use char::CharExt;
 use cmp::{Eq, PartialOrd};
+use convert::From;
 use fmt;
 use intrinsics;
 use marker::{Copy, Sized};
@@ -1471,3 +1472,45 @@ impl fmt::Display for ParseIntError {
 }
 
 pub use num::dec2flt::ParseFloatError;
+
+// Conversion traits for primitive integer types
+// Conversions T -> T are covered by a blanket impl and therefore excluded
+// Some conversions from and to usize/isize are not implemented due to portability concerns
+macro_rules! impl_from {
+    ($Small: ty, $Large: ty) => {
+        #[stable(feature = "lossless_int_conv", since = "1.5.0")]
+        impl From<$Small> for $Large {
+            #[stable(feature = "lossless_int_conv", since = "1.5.0")]
+            #[inline]
+            fn from(small: $Small) -> $Large {
+                small as $Large
+            }
+        }
+    }
+}
+
+// Unsigned -> Unsigned
+impl_from! { u8, u16 }
+impl_from! { u8, u32 }
+impl_from! { u8, u64 }
+impl_from! { u8, usize }
+impl_from! { u16, u32 }
+impl_from! { u16, u64 }
+impl_from! { u32, u64 }
+
+// Signed -> Signed
+impl_from! { i8, i16 }
+impl_from! { i8, i32 }
+impl_from! { i8, i64 }
+impl_from! { i8, isize }
+impl_from! { i16, i32 }
+impl_from! { i16, i64 }
+impl_from! { i32, i64 }
+
+// Unsigned -> Signed
+impl_from! { u8, i16 }
+impl_from! { u8, i32 }
+impl_from! { u8, i64 }
+impl_from! { u16, i32 }
+impl_from! { u16, i64 }
+impl_from! { u32, i64 }