test.rs

#![feature(default_type_params)]
use std::thunk::Invoke;

struct Foo {
    f: Box<for<'a> Invoke<&'a [u8]> + Send>,
}

impl Foo {
    fn new<F> (f: F) -> Foo where F: FnOnce(&[u8]), F: Send {
        Foo { f: box f }
    }

    fn foo (self) {
        let data: [u8, ..4] = [1, 2, 3, 4];
        let data_ref: &[u8] = data.as_slice();
        self.f.invoke(data_ref);
    }
}

fn main () {
    let foo = Foo::new(|data| {
        println!("Foo data: {}", data);
    });
    foo.foo();
}