instance: add hostport selection methods

instance: add hostport selection methods

Theoretically we could call Select*Address and then
search through the slice for the right address instead,
but doing it this way is more convenient and more
efficient.

https://code.launchpad.net/~rogpeppe/juju-core/523-instance-select-hostport/+merge/211570

(do not edit description out of merge proposal)

[rog, 2014-03-18 16:15:28]

Please take a look.

[natefinch, 2014-03-18 17:14:46]

This seems like an overly complex refactoring of the code just to avoid having
to extract a list of addresses from a list of hostports.... lists that are
probably almost always 1-4 items long.  The code look correct, I just don't
think it's worth the complexity of creating anonymous functions to return the
address rather than just making a list of addresses when we need to do it with
hostports.

[natefinch, 2014-03-18 17:28:03]

On 2014/03/18 17:14:46, nate.finch wrote:
> This seems like an overly complex refactoring of the code just to avoid having
> to extract a list of addresses from a list of hostports.... lists that are
> probably almost always 1-4 items long.  The code look correct, I just don't
> think it's worth the complexity of creating anonymous functions to return the
> address rather than just making a list of addresses when we need to do it with
> hostports.

Actually, scratch that, I see you're returning the NetAddr of hostports, not
just the Address's Value.  Still seems like something that would be simpler to
accomplish using an interface they both implement rather than passing functions
and all that... but I guess it LGTM as is.

[rog, 2014-03-18 18:42:59]

On 18 March 2014 17:14,  <nate.finch@gmail.com> wrote:
> This seems like an overly complex refactoring of the code just to avoid
> having to extract a list of addresses from a list of hostports.... lists
> that are probably almost always 1-4 items long.  The code look correct,
> I just don't think it's worth the complexity of creating anonymous
> functions to return the address rather than just making a list of
> addresses when we need to do it with hostports.

That was what I started off doing, but then I realised that
you not only need to extract the addresses - you also need
to map back to the index of the chosen address by scanning
the slice, so you can attach the appropriate port number. That seemed like
it was too much work and a little over-heuristic when
we can do the work directly with a little refactoring.

That's why it turned out like this.