Re: Specifying callbacks for behaviours extending gen_server

Hi Brett,

This may help you out. http://davekuhlman.org/implement-a-behavior.html

Fairly simple example and concise of a behavior wrapping a gen_server

Kind regards,
Leonard

On Tue, Feb 23, 2021 at 11:18 AM Brett Hemes <[email protected]> wrote:
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> Hah; Fernando after I replied I (think I) realized what you were saying.  I now only specify my specific extensions in my behaviour using the `-callback` attribute and then include both my behaviour and gen_server in the user modules via `-behaivour`.  I think this is a good solution to my dilemma.
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> Thanks!
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> Brett
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> From: erlang-questions <[email protected]> On Behalf Of Brett Hemes
> Sent: Tuesday, February 23, 2021 10:08 AM
> To: [email protected]
> Subject: [EXTERNAL] Re: Specifying callbacks for behaviours extending gen_server
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> 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.
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> 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.
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> Brett
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> From: Fernando Benavides <[email protected]>
> Sent: Tuesday, February 23, 2021 9:26 AM
> To: Brett Hemes <[email protected]>
> Cc: [email protected]
> Subject: [EXTERNAL] Re: Specifying callbacks for behaviours extending gen_server
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> What if you only specify your own callbacks and let your implementors use...
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> -behavior(your behavior).
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> -behavior(gen_server).
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> ?
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> On Tue, 23 Feb 2021 at 16:15 Brett Hemes <[email protected]> wrote:
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> 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
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> > behaviour_info(Type) -> gen_server:behaviour_info(Type).
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> 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?
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> Thanks,
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> Brett
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> --
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