Returned lifetimes are too restrictive.

[Dirbaio]

If you call a method on a Local<'env, Foo>, it gets borrowed for a new shorter lifetime 'short, and deref'd to &'short Foo. The method then returns a Local<'short, Bar>.

This is unnecessarily restrictive, it could return a Local<'env, Bar>, Returning Local<'short, Bar> is annoying, for example it prevents moving or destroying the original Foo while the Bar is live.

I have prototyped a possible solution using arbitrary self types. Methods take self: Ref<'env, Self> instead of &self, so they can "see" the original 'env lifetime and return Local<'env>. Seems it works nicely so far. See branch: https://github.com/Dirbaio/java-spaghetti/tree/receiver

There's a newer RFC for arbitrary self types v2, hopefully there's a push to stabilize it soon. rust-lang/rfcs#3519

I don't know if there's a reasonably ergonomic way of solving this without arbitrary self types. Solutions are welcome.

[Dirbaio]

Updated receiver branch to use arbitrary self types v2. Works pretty great!

[wuwbobo2021]

You have pointed out that the Deref implementation for Local<'env, T> is unsound in release version 0.2.0: "this is unsound because Ref can be cloned/copied. You can get a Ref out of the Local, copy it, drop the Local, then use-after-free through the Ref." Thank you very much!

It seems like your solution for this problem requires the Rust "arbitrary_self_types" feature, hopefully this will be stabilized in Rust 1.86 (I'm not sure): rust-lang/rust#135881

[Dirbaio]

yep! I actually didn't realize it also affects the main branch. Maybe the same fix (make Ref not Copy/Clone, make everything take &Ref instead of Ref) should work on main, but the ObjectAndEnv hack makes it much more annoying.

[Dirbaio]

i've merged receiver into main, so this is now fixed.

Not sure whether to wait until arbitrary_self_types is stable for a release or what