Bounds

Just like generic types can be bounded, lifetimes (themselves generic) use bounds as well. The : character has a slightly different meaning here, but + is the same. Note how the following read:

1. T: 'a: All references in T must outlive lifetime 'a.
2. T: Trait + 'a: Type T must implement trait Trait and all references in T must outlive 'a.

The example below shows the above syntax in action used after keyword where:

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See also:

generics, bounds in generics, and multiple bounds in generics