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document #![feature(const_generics_defaults)] #1098

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Feb 8, 2022
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5 changes: 3 additions & 2 deletions src/items/generics.md
Original file line number Diff line number Diff line change
Expand Up @@ -15,14 +15,14 @@
> &nbsp;&nbsp; [IDENTIFIER]( `:` [_TypeParamBounds_]<sup>?</sup> )<sup>?</sup> ( `=` [_Type_] )<sup>?</sup>
>
> _ConstParam_:\
> &nbsp;&nbsp; `const` [IDENTIFIER] `:` [_Type_]
> &nbsp;&nbsp; `const` [IDENTIFIER] `:` [_Type_] ( `=` _[Block][block]_ | [IDENTIFIER] | -<sup>?</sup>[LITERAL] )<sup>?</sup>

[Functions], [type aliases], [structs], [enumerations], [unions], [traits], and
[implementations] may be *parameterized* by types, constants, and lifetimes. These
parameters are listed in angle <span class="parenthetical">brackets (`<...>`)</span>,
usually immediately after the name of the item and before its definition. For
implementations, which don't have a name, they come directly after `impl`.
The order of generic parameters is restricted to lifetime parameters, then type parameters, and then const parameters.
The order of generic parameters is restricted to lifetime parameters and then type and const parameters intermixed.

Some examples of items with type, const, and lifetime parameters:

Expand All @@ -31,6 +31,7 @@ fn foo<'a, T>() {}
trait A<U> {}
struct Ref<'a, T> where T: 'a { r: &'a T }
struct InnerArray<T, const N: usize>([T; N]);
struct EitherOrderWorks<const N: bool, U>(U);
```

Generic parameters are in scope within the item definition where they are
Expand Down