% Associated Types
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> Associated types are a way of associating a type placeholder with a trait such that the trait method definitions can use these placeholder types in their signatures.
```rust
pub trait Iterator {
type Item;
fn next(&mut self) -> Option;
}
```
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You can find the latest version of this information
[here](ch19-03-advanced-traits.html#specifying-placeholder-types-in-trait-definitions-with-associated-types).