rust 生命周期参数必须比静态生命周期更长

Question

So I'm following this tutorial to build a rogue-like and I've decided to start using the specs dispatcher to make registering and executing systems a bit easier.

To do that I've added aDispatcher to my State struct:

use rltk::{GameState, Rltk};
use specs::world::World;
use specs::Dispatcher;


pub struct State<'a, 'b> {  // <-- Added new lifetime params here for dispacher
    pub ecs: World,
    pub dsp: Dispatcher<'a, 'b>,
}

But it's when I try to implement the GameSate trait for it I run into issues:

impl<'a, 'b> GameState for State<'a, 'b> {
    fn tick(&mut self, ctx: &mut Rltk) {
        ctx.cls();
        self.dsp.dispatch(&mut self.ecs);
        self.ecs.maintain();
    }
}

I get these errors:

error[E0478]: lifetime bound not satisfied
  --> src/sys/state.rs:96:14
   |
96 | impl<'a, 'b> GameState for State<'a, 'b> {
   |              ^^^^^^^^^
   |
note: lifetime parameter instantiated with the lifetime `'a` as defined on the impl at 96:6
  --> src/sys/state.rs:96:6
   |
96 | impl<'a, 'b> GameState for State<'a, 'b> {
   |      ^^
   = note: but lifetime parameter must outlive the static lifetime

error[E0478]: lifetime bound not satisfied
  --> src/sys/state.rs:96:14
   |
96 | impl<'a, 'b> GameState for State<'a, 'b> {
   |              ^^^^^^^^^
   |
note: lifetime parameter instantiated with the lifetime `'b` as defined on the impl at 96:10
  --> src/sys/state.rs:96:10
   |
96 | impl<'a, 'b> GameState for State<'a, 'b> {
   |          ^^
   = note: but lifetime parameter must outlive the static lifetime

It wants the lifetimes 'a, 'b to outlive 'static , which sounds impossible as I'm sure that 'static is the whole program's lifetime.

How do I resolve this?

Answer 1

GameState requires that implementors must be 'static :

pub trait GameState: 'static {...}

In order to satisfy the 'static lifetime, your type must not contain any references shorter than 'static . So, if you can't make 'a and 'b both be 'static , the only option is not to put the Dispatcher inside State .

For lifetime 'a to "outlive 'static " means that 'a must be equal or longer than 'static (and yes, 'static is the longest lifetime possible). Rust issue for a similar error .