A function chooses at runtime between two capturing closure expressions and returns the c…

A function chooses at runtime between two capturing closure expressions and returns the chosen callback. Which return type directly supports this?

1. Box<dyn Fn(i32) -> i32>
2. impl Fn(i32) -> i32 with an unrelated closure in each branch
3. fn(i32) -> i32 for arbitrary capturing closures
4. &dyn Fn(i32) -> i32 borrowed from a local Box