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Rollup merge of #35613 - matthew-piziak:array-docs-trait-justification, r=steveklabnik

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provide additional justification for array interface design

Explain why Rust does not implement traits for large arrays.

Explain why most methods are implemented on slices rather than arrays.

Note: I'm dipping my toes in the water with a tiny PR. Especially looking for feedback on wording and style. Points of concern: appropriate level of top-level explanation; foreshadowing (is it appropriate to imply that we expect Rust's type system to eventually support size-generic arrays?); using `Foo` and `Bar` as type variables instead of e.g. `T` and `S`.

@peschkaj
This commit is contained in:
Jonathan Turner 2016-08-17 06:25:24 -07:00 committed by GitHub
commit 559bfd68e3
1 changed files with 8 additions and 3 deletions
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src/libstd/primitive_docs.rs
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@ -269,13 +269,18 @@ mod prim_pointer { }
/// - `Borrow`, `BorrowMut`
/// - `Default`
///
/// This limitation to `N in 0..33` exists because Rust does not yet support
/// generics over the size of an array type. `[Foo; 3]` and `[Bar; 3]` are
/// instances of same generic type `[T; 3]`, but `[Foo; 3]` and `[Foo; 5]` are
/// entirely different types. As a stopgap, trait implementations are
/// statically generated for `N in 0..33`.
///
/// Arrays coerce to [slices (`[T]`)][slice], so their methods can be called on
/// arrays.
/// arrays. Slices are dynamic and do not coerce to arrays; consequently more
/// methods are defined on `slice` where they support both types.
///
/// [slice]: primitive.slice.html
///
/// Rust does not currently support generics over the size of an array type.
///
/// # Examples
///
/// ```