Not really sure if this is a smart question but:
Why are there no select actions implemented for IO operations?
On first glance, it would simplify things if one could intermix inter fiber communication (channels) with inter process communication (like sockets) in select statements.
What did I miss?
It looks like select actions are only implemented for Channel.
➜ crystal git:(master) ✗ ag 'def \w+_select_action' src
src/channel.cr
508: def send_select_action(value : T)
513: def receive_select_action
518: def receive_select_action?
765:def timeout_select_action(timeout : Time::Span) : Channel::TimeoutAction
So I think, more than than not being implemented for IO specifically, it’s that they haven’t been implemented for anything else (yet?).
What kinds of select actions are you looking for? I’ve had limited need for them (though I have needed them), so I’m legitimately curious.
select doesn’t seem like it’s needed for this because we have better things like IO#peek [IO - Crystal 1.13.1] that would better to use than select would. select exists because Channel only has send and receive which is a big deal because we don’t have any non-blocking way to check if a channel has things waiting in it, if it needs a timeout, or if its empty or not. At the same time, you can enact anything you need to do with any IO though a Channel as well, which may be needed if you are doing something multi-fiber with the results of an IO. There are a lot of ways to skin that cat and it should be left up to the system designer to design how that should work.
FYI: the select expression isn’t related to the select(2) syscall, but to the select expression from Go that only works with channels.
This can be used for your use case: spawn a fiber that waits on the socket and sends the message through a channel that you can select on.
IMO: we shouldn’t document how select actions are implemented. First it’s an implementation detail, and second you can’t write your own actions anyway, because you must implement undocumented abstract types that are private to Channel.