WindowHandler lifetime issue

[d0rianb]

I can't figure out how to use references in struct belonging to the WindowHandler because of lifetime errors : error[E0759]: `self` has an anonymous lifetime `'_` but it needs to satisfy a `'static` lifetime requirement'. The WindowHandler lifetime is suppose to be static because it lives as long as the program lives but there is no way to specify it to the compiler. I try by changing the 'static lifetime on the Context into anonymous but it's still the same error. Is it any solution ? A simple replication of my issue is down below :

use speedy2d::window::{KeyScancode, VirtualKeyCode, WindowHandler, WindowHelper};
use speedy2d::Window;

fn main() {
    let window = Window::new_centered("Speedy2D: test", (800, 600)).unwrap();

    window.run_loop(MyWindowHandler {
        context: Context { blocks: vec![Block {}], selected_block: &Block {} },
    })
}

struct Block;

struct Context<'ctx> {
    blocks: Vec<Block>,
    selected_block: &'ctx Block,
}

impl<'ctx> Context<'ctx> {
    pub fn add_selected_block(&'ctx mut self) {
        self.selected_block = &self.blocks[0];
    }
}

struct MyWindowHandler {
    context: Context<'static>,
}

impl WindowHandler for MyWindowHandler {
    fn on_key_down(&mut self, _helper: &mut WindowHelper, _virtual_key_code: Option<VirtualKeyCode>, _scancode: KeyScancode) {
        self.context.add_selected_block();
    }
}

[QuantumBadger]

Hi @d0rianb, I think what you're trying to do is forbidden by Rust.

struct Context<'ctx> {
    blocks: Vec<Block>,
    selected_block: &'ctx Block,
}

In Rust, self-referential structs are forbidden -- in other words, it's not possible to have a struct hold a reference to a thing which is also in that struct. I'd recommend changing this to:

struct Context {
    blocks: Vec<Rc<Block>>,
    selected_block: Rc<Block>,
}

Or alternatively, selected_block could be an integer or other ID, which shows which block in the Vec is selected.

[d0rianb]

Ok I will try this but I don't think it's a self-referential struct because selected_block refer to a Block not to the context.

[QuantumBadger]

I think a self-referential struct just means any struct which has a reference to either itself, or something inside itself.

To give a specific example of the safety issue, let's say you set self.selected_block to &self.blocks[0], and then delete all the elements in self.blocks. This would mean self.selected_block now points to something which doesn't exist (i.e. a dangling reference).

[d0rianb]

Ok I understand I will implement the Rc solution, thanks