diff options
| -rw-r--r-- | library/core/src/cmp.rs | 16 |
1 files changed, 10 insertions, 6 deletions
diff --git a/library/core/src/cmp.rs b/library/core/src/cmp.rs index b983f49eb17..4a15b185a83 100644 --- a/library/core/src/cmp.rs +++ b/library/core/src/cmp.rs @@ -31,14 +31,18 @@ use self::Ordering::*; /// equivalence relation. For example, in floating point numbers `NaN != NaN`, /// so floating point types implement `PartialEq` but not [`trait@Eq`]. /// -/// Formally, the equality must be (for all `a`, `b` and `c`): +/// Formally, the equality must be (for all `a`, `b`, `c` of type `A`, `B`, +/// `C`): /// -/// - symmetric: `a == b` implies `b == a`; and -/// - transitive: `a == b` and `b == c` implies `a == c`. +/// - **Symmetric**: if `A: PartialEq<B>` and `B: PartialEq<A>`, then **`a == b` +/// implies `b == a`**; and +/// +/// - **Transitive**: if `A: PartialEq<B>` and `B: PartialEq<C>` and `A: +/// PartialEq<C>`, then **`a == b` and `b == c` implies `a == c`**. /// -/// Note that these requirements mean that the trait itself must be implemented -/// symmetrically and transitively: if `T: PartialEq<U>` and `U: PartialEq<V>` -/// then `U: PartialEq<T>` and `T: PartialEq<V>`. +/// Note that the `B: PartialEq<A>` (symmetric) and `A: PartialEq<C>` +/// (transitive) impls are not forced to exist, but these requirements apply +/// whenever they do exist. /// /// ## Derivable /// |