Specifying callbacks for behaviours extending gen_server

[Brett Hemes]

I was trying out the approach of the first answer here (https://stackoverflow.com/questions/6745183/erlang-extended-gen-server).  In this approach, the extension behaviour get first crack at all of the gen_server messages and then forwards the user-module-specific stuff to the user module’s gen_server implementation.

Basically I have written a bunch of (tested/working) TCP client/server interaction code as a gen_server and have a bunch of other modules that add specific functionality on top but require the same TCP handshaking.  My idea was to wrap my working stuff as a behaviour but I can’t yet decide if I want to expose all of gen_server to my user modules or customize the interface.  Right now I have opted for generality and am experimenting with exposing everything but we shall see...  I am in that awkward place where I am working out my architecture while also trying to learn Erlang best practices; fun times.

Brett

From: Fernando Benavides <elbrujohalcon@REDACTED>
Sent: Tuesday, February 23, 2021 9:26 AM
To: Brett Hemes <brhemes@REDACTED>
Cc: erlang-questions@REDACTED
Subject: [EXTERNAL] Re: Specifying callbacks for behaviours extending gen_server

What if you only specify your own callbacks and let your implementors use...

-behavior(your behavior).
-behavior(gen_server).

?

On Tue, 23 Feb 2021 at 16:15 Brett Hemes <brhemes@REDACTED<mailto:brhemes@REDACTED>> wrote:
I am designing a behaviour that extends gen_server and thus I want all of gen_server’s callback specification in addition to some additional ones on top as part of the extension.  In the past I have favored using the `-callback` attribute as recommended in the documentation but then I saw someone recommend the following when extending gen_server

> behaviour_info(Type) -> gen_server:behaviour_info(Type).

I tried combining the two approaches but such is not allowed (which makes sense).  I believe my options are to append my callbacks to gen_server’s list using `behaviour_info` or to copy gen_server’s callback specifications from the OTP source.  Copy-pasting code just feels wrong...  how bad is it to use `behaviour_info` over `-callback`?  And am I taking the right approach?

Thanks,
Brett
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