&'static and T: 'static

'static is a reserved lifetime name, you might have encountered it several times:

#![allow(unused)]
fn main() {
// A reference with 'static lifetime:
let s: &'static str = "hello world";

// 'static as part of a trait bound:
fn generic<T>(x: T) where T: 'static {}
}

Though they are all 'static, but subtly different.

&'static

As a reference lifetime, &'static indicates the data pointed to by the reference lives as long as the running program. But it can still be coerced to a shorter lifetime.

  1. 🌟🌟 There are several ways to make a variable with 'static lifetime, two of them are stored in the read-only memory of the binary.
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  1. 🌟🌟🌟🌟 Another way to make 'static lifetime is using Box::leak
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  1. 🌟 &'static only indicates that the data can live forever, not the reference. The latter one will be constrained by its scope.
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  1. &'static can be coerced to a shorter lifetime.

Example

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T: 'static

As a trait bound, it means the type does not contain any non-static references. Eg. the receiver can hold on to the type for as long as they want and it will never become invalid until they drop it.

It's important to understand this means that any owned data always passes a 'static lifetime bound, but a reference to that owned data generally does not.

  1. 🌟🌟
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  1. 🌟🌟🌟
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You can find the solutions here(under the solutions path), but only use it when you need it :)