fn pointer type is not Clone when containing a parameter with an unspecified lifetime

[samfoo]

The following snippet fails to compile.

#[deriving(Clone)]
enum Thing {
    Func(fn(&str) -> String)
}

#[allow(unused_variables)]
fn a(b: &str) -> String {
    "a".to_string()
}

#[allow(unused_variables)]
fn main() {
    let f = Thing::Func(a);

    println!("Good to go!");
}

Yielding the error...

<anon>:3:10: 3:28 error: the trait `core::clone::Clone` is not implemented for the type `fn(&str) -> collections::string::String`
<anon>:3     Func(fn(&str) -> String)
                  ^~~~~~~~~~~~~~~~~~
note: in expansion of #[deriving]
<anon>:1:1: 1:19 note: expansion site

However, it works when the argument reference is given a lifetime specifier (as below).

#[deriving(Clone)]
enum Thing {
    Func(fn(&'static str) -> String)
}

#[allow(unused_variables)]
fn a(b: &'static str) -> String {
    "a".to_string()
}

#[allow(unused_variables)]
fn main() {
    let f = Thing::Func(a);

    println!("Good to go!");
}

Good to go!

Structs/enums cloneability should not rely on the lifetime of a bare function's arguments, since the argument's lifetime is relative to the function, not the struct.

Compiler version details:

$ rustc --version --verbose
rustc 0.13.0-nightly (10d99a973 2014-12-31 21:01:42 +0000)
binary: rustc
commit-hash: 10d99a973498c5a1be6ba318210751efc1c2cf61
commit-date: 2014-12-31 21:01:42 +0000
host: x86_64-apple-darwin
release: 0.13.0-nightly

[fengsp]

I have got the same error, is this a bug or what? I just can not clone any function that takes a reference.

[gaudecker]

I ran into the same error.

[blaenk]

Note that if you contain types in the fn signature that are from your own crate, you can provide an explicit implementation yourself as a workaround. That doesn't solve this in the general case though, such as in the example in the first post, since neither &str nor String are from your own crate.

[steveklabnik]

Traige: new code:

#[derive(Clone)]
enum Thing {
    Func(fn(&str) -> String)
}

#[allow(unused_variables)]
fn a(b: &str) -> String {
    "a".to_string()
}

#[allow(unused_variables)]
fn main() {
    let f = Thing::Func(a);

    println!("Good to go!");
}

[nikomatsakis]

Fixed now, thanks to @scalexm's PR for #44490. I believe there exist enough tests, so just going to close.