Named functions don't implement Debug

[asajeffrey]

Trying to compile (https://play.rust-lang.org/?gist=3b38f384f0f7ddecc142&version=stable):

fn foo() {}
fn main() {
    println!("{:?}", (foo as fn())); // Works
    println!("{:?}", foo);   // Fails
} 

It seem that named functions have to be coerced to anonymous ones in order to implement Debug. This means any structs containing functions don't derive Debug, which makes unit testing tricky.

[durka]

I guess it would have to be an impl-by-compiler-magic since they are all separate types. Would you expect it to print out the memory address like the casted version (which, as I understand it, may not even exist due to inlining etc) or the function name?

[asajeffrey]

The function name would be best, even just "..." would be fine, currently we can't use unit tests with assert_eq with any type which contains a named function.

[steveklabnik]

Triage: this is still true today.