Function cookie_factory::cond

pub fn cond<F, I: Write>(condition: bool, f: F) -> impl SerializeFn<I> where
    F: SerializeFn<I>, 

Applies a serializer if the condition is true

use cookie_factory::{cond, string};

let mut buf = [0u8; 100];

{
  let buf = cond(true, string("abcd"))(&mut buf[..]).unwrap();
  assert_eq!(buf.len(), 100 - 4);
}

assert_eq!(&buf[..4], &b"abcd"[..]);