我如何在 rust 实现中为具有 static 生命周期的特征指定结构生命周期？

Question

I have this code:

// engine.rs
pub struct Engine<'a, 'b> {
    // ...some code
    dispatcher: Dispatcher<'a, 'b>
}

impl<'a, 'b> GameState for Engine<'a, 'b> { // <- Error
    fn tick(&mut self, ctx: &mut BTerm) {
        todo!()
    }
}

// dispatcher.rs (lib file)
pub struct Dispatcher<'a, 'b> {
    //...some code
}

// gamestate.rs (lib file)
pub trait GameState: 'static {
    fn tick(&mut self, ctx: &mut BTerm);
}

I need the dispatcher field in the structure, but when specifying the field type, I also need to specify the lifetime. This is not a problem as long as I don't have to specify a lifetime in the GameState implementation block which has a static lifetime. When I try to specify the lifetime there, I get an error. I can't change the GameState and Dispatcher because it's library code and I need the dispatcher field in the struct. How can I solve this problem?

Full error text:

error[E0478]: lifetime bound not satisfied
  --> src/engine.rs:14:14
   |
14 | impl<'a, 'b> GameState for Engine<'a, 'b> {
   |              ^^^^^^^^^
   |
note: lifetime parameter instantiated with the lifetime `'b` as defined here
  --> src/engine.rs:14:10
   |
14 | impl<'a, 'b> GameState for Engine<'a, 'b> {
   |          ^^
   = note: but lifetime parameter must outlive the static lifetime

Answer 1

You have to define all lifetimes that Engine contains as 'static because by writing trait Gamestate: 'static you say that Gamestate can only be implemented for things that contain no references that live shorter than 'static but by trying to define it for a struct containing references of a generic lifetime 'a which you have to assume can be any lifetime in practice this obviously isn't fulfilled.

Wether you do it by directly secifying it in Engine , Dispatcher or by passing 'static as generic parameters is up to you to decide, do you need to support non-static lifetimes in a Engine ? Then you definitely can't use 'static in it's definition, similar for Dispatcher .