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| -rw-r--r-- | src/doc/trpl/glossary.md | 8 | ||||
| -rw-r--r-- | src/doc/trpl/traits.md | 14 |
2 files changed, 16 insertions, 6 deletions
diff --git a/src/doc/trpl/glossary.md b/src/doc/trpl/glossary.md index 106d225d2d0..0956580ade0 100644 --- a/src/doc/trpl/glossary.md +++ b/src/doc/trpl/glossary.md @@ -38,6 +38,14 @@ let z = (8, 2, 6); In the example above `x` and `y` have arity 2. `z` has arity 3. +### Bounds + +Bounds are constraints on a type or [trait][traits]. For example, if a bound +is placed on the argument a function takes, types passed to that function +must abide by that constraint. + +[traits]: traits.html + ### DST (Dynamically Sized Type) A type without a statically known size or alignment. ([more info][link]) diff --git a/src/doc/trpl/traits.md b/src/doc/trpl/traits.md index 6ba0f287be3..7b6d0b730a3 100644 --- a/src/doc/trpl/traits.md +++ b/src/doc/trpl/traits.md @@ -47,12 +47,14 @@ As you can see, the `trait` block looks very similar to the `impl` block, but we don’t define a body, just a type signature. When we `impl` a trait, we use `impl Trait for Item`, rather than just `impl Item`. -## Trait constraints on generic functions +## Trait bounds on generic functions Traits are useful because they allow a type to make certain promises about its -behavior. Generic functions can exploit this to constrain the types they +behavior. Generic functions can exploit this to constrain, or [bound][bounds], the types they accept. Consider this function, which does not compile: +[bounds]: glossary.html#bounds + ```rust,ignore fn print_area<T>(shape: T) { println!("This shape has an area of {}", shape.area()); @@ -66,7 +68,7 @@ error: no method named `area` found for type `T` in the current scope ``` Because `T` can be any type, we can’t be sure that it implements the `area` -method. But we can add a ‘trait constraint’ to our generic `T`, ensuring +method. But we can add a trait bound to our generic `T`, ensuring that it does: ```rust @@ -155,10 +157,10 @@ We get a compile-time error: error: the trait `HasArea` is not implemented for the type `_` [E0277] ``` -## Trait constraints on generic structs +## Trait bounds on generic structs -Your generic structs can also benefit from trait constraints. All you need to -do is append the constraint when you declare type parameters. Here is a new +Your generic structs can also benefit from trait bounds. All you need to +do is append the bound when you declare type parameters. Here is a new type `Rectangle<T>` and its operation `is_square()`: ```rust |