#![feature(unboxed_closures, core)]

pub struct Foo<T> { t: T }

impl<'a, T> Foo<T> where T: 'a + FnMut() -> &'a [u8] {
    pub fn from_callback(closure: T) -> Self {
        Foo { t: closure }
    }

    pub fn work(&mut self) {
      println!("{:?}", self.t.call_mut(()));
      println!("{:?}", self.t.call_mut(()));
    }
}

fn main() {
  let mut foo = {
    let buffer = vec![1, 2, 3, 4];
    let mut i = 0;
    Foo::from_callback(move || {
      let j = i;
      i += 1;
      &buffer[j..j+1]
    })
  };
  foo.work();
}