Compiler version

cc-experiment branch

Minimized code

trait Cap { def use(): Int } type Id[X] = [T] -> (op: X => T) -> T def mkId[X](x: X): Id[X] = [T] => (op: X => T) => op(x) def bar() = { def withCap[X](op: ({*} Cap) => X): X = { val cap: {*} Cap = new Cap { def use() = { println("cap is used"); 0 } } val result = op(cap) result } val leak = withCap(cap => mkId(cap)) leak { cap => cap.use() } // bad }

Output

It compiles.

Expectation

It should not compile. We expect the type of val leak to be Id[□ {*} Cap], so it will expect a function of (□ {*} Cap) => Unit in leak(...). It will not be possible to adapt cap => cap.use() : ({*} Cap) -> Unit to the type (□ {*} Cap) => Unit since the adaption cap => (unbox cap).use() tries to unbox a reference capturing universal capability.

We should issue an error on leak(...).