auto merge of #7142 : alexcrichton/rust/deriving-zero, r=pcwalton

This allows mass-initialization of large structs without having to specify all the fields.

I'm a bit hesitant, but I wanted to get this out there. I don't really like using the `Zero` trait, because it doesn't really make sense for a type like `HashMap` to use `Zero` as the 'blank allocation' trait. In theory there'd be a new trait, but then that's adding cruft to the language which may not necessarily need to be there.

I do think that this can be useful, but I only implemented `Zero` on the basic types where I thought it made sense, so it may not be all that usable yet. (opinions?)

1 files changed, 15 insertions, 0 deletions

diff --git a/src/libstd/num/num.rs b/src/libstd/num/num.rs
index a9893579721..4681e4f4f53 100644
--- a/src/libstd/num/num.rs
+++ b/src/libstd/num/num.rs
@@ -418,6 +418,21 @@ pub fn pow_with_uint<T:NumCast+One+Zero+Copy+Div<T,T>+Mul<T,T>>(radix: uint, pow
     total
 }
 
+impl<T: Zero> Zero for @mut T {
+    fn zero() -> @mut T { @mut Zero::zero() }
+    fn is_zero(&self) -> bool { (**self).is_zero() }
+}
+
+impl<T: Zero> Zero for @T {
+    fn zero() -> @T { @Zero::zero() }
+    fn is_zero(&self) -> bool { (**self).is_zero() }
+}
+
+impl<T: Zero> Zero for ~T {
+    fn zero() -> ~T { ~Zero::zero() }
+    fn is_zero(&self) -> bool { (**self).is_zero() }
+}
+
 /// Helper function for testing numeric operations
 #[cfg(test)]
 pub fn test_num<T:Num + NumCast>(ten: T, two: T) {