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Clarify the English translation of ?Sized

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* It wasn't clear whether `?Sized` meant "not `Sized`" or "`Sized` or not `Sized`". According to #rust IRC, it does indeed mean "`Sized` or not `Sized`".
* Use the same language as [Trait std::marker::Sized](https://doc.rust-lang.org/std/marker/trait.Sized.html) about how `Sized` is implicitly bound.
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Postmodern 2016-05-19 17:07:29 -07:00
parent 764ef92ae7
commit 2fd4e604a4
1 changed files with 3 additions and 4 deletions
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7
src/doc/book/unsized-types.md
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@ -47,7 +47,7 @@ pointers, can use this `impl`.
# ?Sized
If you want to write a function that accepts a dynamically sized type, you
can use the special bound, `?Sized`:
can use the special syntax, `?Sized`:
```rust
struct Foo<T: ?Sized> {
@ -55,6 +55,5 @@ struct Foo<T: ?Sized> {
}
```
This `?`, read as “T may be `Sized`”, means that this bound is special: it
lets us match more kinds, not less. It’s almost like every `T` implicitly has
`T: Sized`, and the `?` undoes this default.
This `?Sized`, read as “T may or may not be `Sized`”, allowing us to match both constant size and unsized types.
All generic type parameters implicitly have the `Sized` bound, so `?Sized` can be used to opt-out of the implicit bound.