Using declare_types with explicit lifetime

[jugglingcats]

I believe this is a direct consequence of rust-lang/rust#34303 which hopefully will be fixed, but am adding here for awareness.

It doesn't seem possible to have a lifetime on the underlying struct for a Javascript class, eg:

pub struct TestMe<'a> {
    x: &'a mut i32
}

declare_types! {
    pub class JsTestMe for TestMe {
        init(call) {
            Ok(TestMe {x: &5})
        }
    }
}

This fails with compile error:

error[E0107]: wrong number of lifetime parameters: expected 1, found 0
  --> src\shm/mod.rs:99:35
   |
99 |     pub class JsTestMe for TestMe {
   |                                   ^ expected 1 lifetime parameter

[eira-fransham]

Workaround: use pub class JsTestMe as TestMe for TestMe<'static>. There is no way to do this with a generic parameter right now, but you can make it concrete.

[ryantate13]

Is it possible to get this to work with lifetimes other than 'static? I get a use of undeclared lifetime name error when I try.

[kjvalencik]

@ryantate13 It is not because the lifetime must be 'static. The object is being handed over to v8 for tracking and garbage collection. Therefore, it must be bounded by the 'static lifetime. I.e., the struct must be capable of being held for the entirety of the program.

If the struct were valid for a shorter time period, it might become invalid while it is still being held by Javascript. Dereferencing this struct would be a use-after-free bug.

Referencing counting (e.g., Arc) is a common way to upgrade something to a 'static lifetime.

I'm going to close this issue because it sounds like 'static is already supported and lifetimes other than 'static cannot be supported.