bianchidotdev
I came across a blog post that implemented a function guard for a liveview socket connection’s presence. It seems like a really ergonomic way to separate out mount functions for connected sockets and disconnected sockets, and I was surprised I wasn’t able to find any existing proposals or suggestions to implement connected? as a macro (very possibly my search fu failing me).
Is there any appetite in implementing this function guard in core liveview? Are there reasons it’s not implemented as a guard yet.
Code referenced in the blog post:
defguard is_connected?(socket) when socket.transport_pid != nil
Enabling:
def mount(params, session, socket) when is_connected?(socket) do
# Connected mount
end
def mount(params, session, socket) do
# Disconnected mount
end
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al2o3cr
One reason this may not exist already - the
map.fieldnotation wasn’t supported in guards until this PR, released in 1.11:https://github.com/elixir-lang/elixir/pull/9711
Phoenix 1.6 only requires Elixir 1.9+, so Phoenix 1.7 is the earliest version this guard could have been included in.
D4no0
definetly some new feature I didn’t see yet
JohnnyCurran
Glad you liked the article! I have been thinking about making a PR to add it to LiveView. I wanted to get some feedback on it first. I suppose this thread might serve that purpose
I haven’t tested it, but I imagine the map.field syntax could be worked around by matching on the fields in the struct:
But that’s just a guess. I wrote that in the forum post editor
codeanpeace
Gave it a whirl and it doesn’t look like you can pattern match when defining guards:
** (ArgumentError) invalid syntax in defguard is_connected?(%Socket{transport_pid: transport_pid})JohnnyCurran
Thanks for giving it a shot though!
I guess that makes sense because guards have to be compile time constants and pattern matching is not