CODEWITHSUNDEEP
ruststatictraitslifetime
Thermatix
Thermatix

Reputation: 2929

rust lifetime parameter must outlive the static lifetime

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 a Dispatcher 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?

Upvotes: 6

Views: 14805

Answers (1)

trent
trent

Reputation: 28075

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.

Upvotes: 5

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