6 files changed, 52 insertions, 56 deletions
diff --git a/src/libstd/bool.rs b/src/libstd/bool.rs
index d080262ccc7..af745f94fb5 100644
--- a/src/libstd/bool.rs
+++ b/src/libstd/bool.rs
@@ -40,7 +40,6 @@ use num::FromPrimitive;
 #[cfg(not(test))] use cmp::{Eq, Ord, TotalOrd, Ordering};
 #[cfg(not(test))] use ops::{Not, BitAnd, BitOr, BitXor};
 #[cfg(not(test))] use default::Default;
-#[cfg(not(test))] use num::Zero;
 
 /////////////////////////////////////////////////////////////////////////////
 // Freestanding functions
@@ -309,12 +308,6 @@ impl Default for bool {
     fn default() -> bool { false }
 }
 
-#[cfg(not(test))]
-impl Zero for bool {
-    fn zero() -> bool { false }
-    fn is_zero(&self) -> bool { *self == false }
-}
-
 #[cfg(test)]
 mod tests {
     use prelude::*;
diff --git a/src/libstd/char.rs b/src/libstd/char.rs
index 4e9c72de618..71a297d7176 100644
--- a/src/libstd/char.rs
+++ b/src/libstd/char.rs
@@ -22,7 +22,6 @@ use str;
 
 #[cfg(not(test))] use cmp::{Eq, Ord};
 #[cfg(not(test))] use default::Default;
-#[cfg(not(test))] use num::Zero;
 
 // UTF-8 ranges and tags for encoding characters
 static TAG_CONT: uint = 128u;
@@ -449,15 +448,6 @@ impl Default for char {
     fn default() -> char { '\x00' }
 }
 
-#[cfg(not(test))]
-impl Zero for char {
-    #[inline]
-    fn zero() -> char { '\x00' }
-
-    #[inline]
-    fn is_zero(&self) -> bool { *self == '\x00' }
-}
-
 #[test]
 fn test_is_lowercase() {
     assert!('a'.is_lowercase());
diff --git a/src/libstd/iter.rs b/src/libstd/iter.rs
index fcf0f4f2444..8081c6ed8db 100644
--- a/src/libstd/iter.rs
+++ b/src/libstd/iter.rs
@@ -2872,6 +2872,12 @@ mod tests {
             }
         }
 
+        impl Mul<Foo, Foo> for Foo {
+            fn mul(&self, _: &Foo) -> Foo {
+                Foo
+            }
+        }
+
         impl num::One for Foo {
             fn one() -> Foo {
                 Foo
diff --git a/src/libstd/num/mod.rs b/src/libstd/num/mod.rs
index c374d6c2157..23a852cc357 100644
--- a/src/libstd/num/mod.rs
+++ b/src/libstd/num/mod.rs
@@ -50,19 +50,59 @@ pub trait Orderable: Ord {
 /// Returns the number constrained within the range `mn <= self <= mx`.
 #[inline(always)] pub fn clamp<T: Orderable>(value: T, mn: T, mx: T) -> T { value.clamp(&mn, &mx) }
 
-pub trait Zero {
-    fn zero() -> Self;      // FIXME (#5527): This should be an associated constant
+/// Defines an additive identity element for `Self`.
+///
+/// # Deriving
+///
+/// This trait can be automatically be derived using `#[deriving(Zero)]`
+/// attribute. If you choose to use this, make sure that the laws outlined in
+/// the documentation for `Zero::zero` still hold.
+pub trait Zero: Add<Self, Self> {
+    /// Returns the additive identity element of `Self`, `0`.
+    ///
+    /// # Laws
+    ///
+    /// ~~~
+    /// a + 0 = a       ∀ a ∈ Self
+    /// 0 + a = a       ∀ a ∈ Self
+    /// ~~~
+    ///
+    /// # Purity
+    ///
+    /// This function should return the same result at all times regardless of
+    /// external mutable state, for example values stored in TLS or in
+    /// `static mut`s.
+    // FIXME (#5527): This should be an associated constant
+    fn zero() -> Self;
+
+    /// Returns `true` if `self` is equal to the additive identity.
     fn is_zero(&self) -> bool;
 }
 
-/// Returns `0` of appropriate type.
+/// Returns the additive identity, `0`.
 #[inline(always)] pub fn zero<T: Zero>() -> T { Zero::zero() }
 
-pub trait One {
-    fn one() -> Self;       // FIXME (#5527): This should be an associated constant
+/// Defines a multiplicative identity element for `Self`.
+pub trait One: Mul<Self, Self> {
+    /// Returns the multiplicative identity element of `Self`, `1`.
+    ///
+    /// # Laws
+    ///
+    /// ~~~
+    /// a * 1 = a       ∀ a ∈ Self
+    /// 1 * a = a       ∀ a ∈ Self
+    /// ~~~
+    ///
+    /// # Purity
+    ///
+    /// This function should return the same result at all times regardless of
+    /// external mutable state, for example values stored in TLS or in
+    /// `static mut`s.
+    // FIXME (#5527): This should be an associated constant
+    fn one() -> Self;
 }
 
-/// Returns `1` of appropriate type.
+/// Returns the multiplicative identity, `1`.
 #[inline(always)] pub fn one<T: One>() -> T { One::one() }
 
 pub trait Signed: Num
@@ -993,16 +1033,6 @@ pub fn from_str_radix<T: FromStrRadix>(str: &str, radix: uint) -> Option<T> {
     FromStrRadix::from_str_radix(str, radix)
 }
 
-impl<T: Zero + 'static> 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() }
-}
-
 /// Saturating math operations
 pub trait Saturating {
     /// Saturating addition operator.
diff --git a/src/libstd/tuple.rs b/src/libstd/tuple.rs
index 313fd9c79b4..8e278aeb2ea 100644
--- a/src/libstd/tuple.rs
+++ b/src/libstd/tuple.rs
@@ -15,7 +15,6 @@
 use clone::Clone;
 #[cfg(not(test))] use cmp::*;
 #[cfg(not(test))] use default::Default;
-#[cfg(not(test))] use num::Zero;
 
 /// Method extensions to pairs where both types satisfy the `Clone` bound
 pub trait CopyableTuple<T, U> {
@@ -177,18 +176,6 @@ macro_rules! tuple_impls {
                     ($({ let x: $T = Default::default(); x},)+)
                 }
             }
-
-            #[cfg(not(test))]
-            impl<$($T:Zero),+> Zero for ($($T,)+) {
-                #[inline]
-                fn zero() -> ($($T,)+) {
-                    ($({ let x: $T = Zero::zero(); x},)+)
-                }
-                #[inline]
-                fn is_zero(&self) -> bool {
-                    $(self.$get_ref_fn().is_zero())&&+
-                }
-            }
         )+
     }
 }
diff --git a/src/libstd/unit.rs b/src/libstd/unit.rs
index c27f6e3d086..786a7f42bb3 100644
--- a/src/libstd/unit.rs
+++ b/src/libstd/unit.rs
@@ -12,8 +12,6 @@
 
 #[cfg(not(test))]
 use prelude::*;
-#[cfg(not(test))]
-use num::Zero;
 
 #[cfg(not(test))]
 impl Eq for () {
@@ -46,11 +44,3 @@ impl Default for () {
     #[inline]
     fn default() -> () { () }
 }
-
-#[cfg(not(test))]
-impl Zero for () {
-    #[inline]
-    fn zero() -> () { () }
-    #[inline]
-    fn is_zero(&self) -> bool { true }
-}