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 ba7950a7097..e95410ba648 100644 --- a/library/core/src/cmp.rs +++ b/library/core/src/cmp.rs @@ -921,14 +921,18 @@ pub macro Ord($item:item) { /// easy to accidentally make them disagree by deriving some of the traits and manually /// implementing others. /// -/// The comparison must satisfy, for all `a`, `b` and `c`: +/// The comparison relations must satisfy the following conditions +/// (for all `a`, `b`, `c` of type `A`, `B`, `C`): /// -/// - transitivity: `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`. -/// - duality: `a < b` if and only if `b > a`. +/// - **Transitivity**: if `A: PartialOrd<B>` and `B: PartialOrd<C>` and `A: +/// PartialOrd<C>`, then `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`. +/// This must also work for longer chains, such as when `A: PartialOrd<B>`, `B: PartialOrd<C>`, +/// `C: PartialOrd<D>`, and `A: PartialOrd<D>` all exist. +/// - **Duality**: if `A: PartialOrd<B>` and `B: PartialOrd<A>`, then `a < b` if and only if `b > a`. /// -/// Note that these requirements mean that the trait itself must be implemented symmetrically and -/// transitively: if `T: PartialOrd<U>` and `U: PartialOrd<V>` then `U: PartialOrd<T>` and `T: -/// PartialOrd<V>`. +/// Note that the `B: PartialOrd<A>` (dual) and `A: PartialOrd<C>` +/// (transitive) impls are not forced to exist, but these requirements apply +/// whenever they do exist. /// /// Violating these requirements is a logic error. The behavior resulting from a logic error is not /// specified, but users of the trait must ensure that such logic errors do *not* result in |