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

[Richard Carlsson]

Using code:is_loaded/1 has the same roundtrip overhead as
code:ensure_loaded(), so in that case you can just use the latter directly
without any extra check.

But as I see it, the warning should just be seen as a pointer for average
users to primarily use the code module, and not as a warning about this
function possibly going away or being bad for you, as long as you know what
you are using it for.


        /Richard

2018-03-07 8:24 GMT+01:00 Michael Truog <mjtruog@REDACTED>:

> On 03/06/2018 10:54 PM, Metin Akat wrote:
>
> Thanks all. I went with the solution Richard proposed. And after testing
> of the full implementation, this check is certainly not the bottleneck of
> the system, as Jesper suggested.
>
>
> The only problem with that, is that the documentation specifies that
> erlang:module_loaded/1 is only really meant to be used by the code server
> (at http://erlang.org/doc/man/erlang.html#module_loaded-1).  If that
> bothers you, you should use the function code:is_loaded/1 instead.
>
>
>
>
>>
>> On Tue, Mar 6, 2018, at 12:23 PM, Richard Carlsson wrote:
>>
>> I was actually considering submitting such a patch a while back, but one
>> argument against making that short-cut could be that operations against the
>> code server should be serialized. On the other hand I haven't yet come up
>> with an example where the short-cut would make a difference that couldn't
>> already happen due to processor scheduling.
>>
>>
>>         /Richard
>>
>> 2018-03-06 16:40 GMT+01:00 Michał Muskała <michal@REDACTED>:
>>
>>
>> On 6 Mar 2018, 16:36 +0100, Richard Carlsson <carlsson.richard@REDACTED>,
>> wrote:
>>
>>
>>
>> is_exported(M, F, A) ->
>>   case erlang:module_loaded(M) of
>>     false -> code:ensure_loaded(M);
>>     true -> ok
>>   end,
>>   erlang:function_exported(M, F, A).
>>
>> (code:ensure_loaded() is slow compared to the fast call to
>> erlang:module_loaded(), even if the module is already in memory).
>>
>>
>>
>> I was recently wondering about this. Is there a reason
>> code:ensure_loaded() does not short circuit using erlang:module_loaded()?
>> It could probably even skip the request to the code server entirely in case
>> the module is already loaded.
>>
>>
>> Michał.
>>
>>
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