Enum HeaderData 

pub enum HeaderData<'a> {
    Str(Box<dyn Iterator<Item = (&'a str, &'a str)> + 'a>),
    Bytes(Box<dyn Iterator<Item = (&'a [u8], &'a [u8])> + 'a>),
    Parsed(Box<dyn Iterator<Item = (&'a HeaderName, &'a HeaderValue)> + 'a>),
}

Internals

We need dyn dispatch for the Iterator contained here since we have no idea at time of usage what the actual type may be. We “could” use three generics for each possible contained concrete Iterator however it would substantially pollute the api. We would need to encode some of the Iterator Item into each usage site, see below.

fn provide_headers<'s, IS, IB, IP>(&'s self, dk: DataKinds) -> Option<HeaderData<'s>>
where IS: Iterator<Item = (&'s str, &'s str)>,
      IB: Iterator<Item = (&'s [u8], &'s [u8])>,
      IP: Iterator<Item = (&'s ::http::HeaderName, &'s ::http::HeaderValue)>;

We tried to use a & dyn Iterator<Item = (..)> here but the issue is on implementation we will be returning a reference to an Iterator created on the stack (without bending over backwards).

Variants

Str(Box<dyn Iterator<Item = (&'a str, &'a str)> + 'a>)

Bytes(Box<dyn Iterator<Item = (&'a [u8], &'a [u8])> + 'a>)

Parsed(Box<dyn Iterator<Item = (&'a HeaderName, &'a HeaderValue)> + 'a>)