[erlang-questions] What is the fastest way to check if a function is defined in a module?

Zachary Kessin zkessin@REDACTED
Sun Mar 4 07:37:03 CET 2018

You can use the function MODULE:module_info/1 something like
is_defined(MyFunc, Arity, MODULE)->
   Functions = MODULE:module_info(functions),
   lists:member({MyFunc,Arity}, Functions).

Where MyFunc is an atom of course

You could also expand that to a call_function_if_defined_with_default/N but
i will leave that to you


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On Sat, Mar 3, 2018 at 9:42 PM, Metin Akat <akat.metin@REDACTED> wrote:

> I'm looking into this code: https://github.com/erlang/otp/blob/master/lib/
> stdlib/src/gen_server.erl#L631
> Seems like this try/catch clause is implemented with the idea that most of
> the time it will succeed, as the callback module will have implemented the
> corresponding callback function, so we will not have to go into the
> exception clause where it needs to call erlang:function_exported/2 one more
> time (presumably as an additional safeguard) which is more expensive than
> an optimistic try clause.
> I am writing something very similar, where such a check (is a function
> exported) will be performed by thousands/millions of processes on every
> message, but in my case... it's quite probable that most of the time this
> WILL raise the exception. In my case the function will be purely optional -
> if defined, it will return a value. If not, a default value will be used.
> So my question is, how bad is this? I will test, but I'm still interested
> if someone has any ideas (maybe do something completely different).
> Other possibilities are:
> - Actually make the callback compulsory. I don't want to do that, as the
> problem I'm solving with this project is "See, you don't have to implement
> this boilerplate every time any more"
> -  Put the option in application env where the user can configure it on
> startup.
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