How to express the lifetime relationship in lambda capture

[vague]

@xmh0511

Box<dyn Trait + 's> mean?

Arc<T> requiring a lifetime for T. Why?

Whenever you write Arc<dyn Trait + 'a>, then this has the following meaning: This Arc can contain any value that implements the Trait trait, and has no lifetime annotations shorter than 'a. When you create the Arc<dyn Trait>, then this is short-hand for Arc<dyn Trait + 'static>, so the compiler must ensure that the actual type has no lifetime annotations shorter than 'static. However, generics are different than dyn Trait (impl Trait is short-hand for generics). When you use generics, they …