What is the plus symbol (+) in generics?

Question

Box<dyn Fn() + Send + 'static>

What does it do and why is there the plus sign (+) in there? I don't remember encountering this in a previous chapter.

How is Box::new(|| println!("hi")) a Box<dyn Fn() + Send + 'static>?

take a look at the [rust by example](https://doc.rust-lang.org/rust-by-example/generics/bounds.html) you also should reread the chapiter 10 of the rust-lang book, the `+` operator is used to combie bounds from cargo doc: ```When working with generics, the type parameters often must use traits as bounds to stipulate what functionality a type implements. For example, the following example uses the trait Display to print and so it requires T to be bound by Display; that is, T must implement Display.``` in your case the `Box` contains a dynamic object that implement `Send` with `'static` lifetime — Asya Corbeau, Oct 08 '19 at 00:19

score 4 · Accepted Answer · answered Oct 08 '19 at 00:42

4

Thanks to @Asya Corbeau pointed me back to chapter 10, it is the Specifying Multiple Trait Bounds with the + Syntax

answered Oct 08 '19 at 00:42

zer09

1 Answers1