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

[Zachary Kessin]

I realize that there is a race condition in that code, if someone reloads
the module at the wrong moment it could crash.



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On Sun, Mar 4, 2018 at 8:37 AM, Zachary Kessin <zkessin@REDACTED> wrote:

> 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
>
> Zach
>
>
> Zach Kessin - CEO Finch Software
> I boost sales with retail chatbots for fashion and cosmetics
> +972 54 234 3956 <054-234-3956> / +44 203 734 9790
> <+44%2020%203734%209790> / +1 617 778 7213 <+1%20617-778-7213>
> Book a meeting with me <https://calendly.com/zkessin/chatbot>
>
> On Sat, Mar 3, 2018 at 9:42 PM, Metin Akat <akat.metin@REDACTED> wrote:
>
>> I'm looking into this code: https://github.com/erlan
>> g/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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>>
>>
>
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