Implement std::num::Zero for bool

Closes #8024.

src/libstd/bool.rs

@@ -24,6 +24,7 @@ Implementations of the following traits:
 * `Ord`
 * `TotalOrd`
 * `Eq`
+* `Zero`
 
 ## Various functions to compare `bool`s
 
@@ -36,14 +37,14 @@ Finally, some inquries into the nature of truth: `is_true` and `is_false`.
 
 */
 
-#[cfg(not(test))]
-use cmp::{Eq, Ord, TotalOrd, Ordering};
-#[cfg(not(test))]
-use ops::Not;
 use option::{None, Option, Some};
 use from_str::FromStr;
 use to_str::ToStr;
 
+#[cfg(not(test))] use cmp::{Eq, Ord, TotalOrd, Ordering};
+#[cfg(not(test))] use ops::Not;
+#[cfg(not(test))] use num::Zero;
+
 /**
 * Negation of a boolean value.
 *
@@ -330,6 +331,12 @@ impl Eq for bool {
     fn ne(&self, other: &bool) -> bool { (*self) != (*other) }
 }
 
+#[cfg(not(test))]
+impl Zero for bool {
+    fn zero() -> bool { false }
+    fn is_zero(&self) -> bool { *self == false }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

src/test/run-pass/deriving-zero.rs

@@ -33,6 +33,7 @@ struct Lots {
     g: (f32, char),
     h: ~[util::NonCopyable],
     i: @mut (int, int),
+    j: bool,
 }
 
 fn main() {