[erlang-questions] Exceptions and gen_server

Anton Krasovsky <>
Sun Nov 8 23:01:58 CET 2009


Thanks for clarifying that, especially throw vs error part!


Regards,
Anton

On Sun, Nov 8, 2009 at 6:47 PM, Robert Virding <> wrote:
> There have been a number of different suggestions as to how you could
> program this. I think the main thing for you to decide is *HOW* you want to
> see the error, then it is relatively easy for you to program it. For
> example:
>
> - First off: do you want the error to crash the server or not? If so is
> links and exit signals a good enough way for you to see the error?
>
> - If the server is to live, how should your app see the error? Two valid
> suggestions which have been given here are:
>
> 1. Signal the error using exit/2. This "simulates" the exit signals as if
> the server had crashed.
> 2. Return an error value which either: returns an error value to the caller;
> or generates an error using erlang:error/1. Which is best for you depends on
> your app.
>
> All these solutions are easy to program so the main problem is for you to
> decide which is best for your app.
>
> One thing I would *NOT* do is use throw/1 to signal error! Throw is for
> non-local returns not errors. Using it for errors will just lead to
> confusion and maybe errors if other parts of app assume it is a non-local
> return. As try can differentiate between throw, exit and error it is
> important that they are used for the right thing.
>
> Robert
>
> P.S. I would LOVE to change catch now so it only catches throws, but I don't
> think it would be possible. :-(
>
> 2009/11/6 Anton Krasovsky <>
>>
>> What would be the standard way of returning/throwing an exception in a
>> result to a gen_server:call?
>>
>> Would something like that be reasonable:
>>
>> a() ->
>> case gen_server:call(..., a) of
>>    {ok, Value} -> Value;
>>    {error, Error} -> throw({error, Error})
>> end
>>
>> and
>>
>> handle_call(a, ...) ->
>> case ... of
>>    {ok, Value} -> {reply, {ok, Value} , State};
>>    {error, Error} -> {reply, {error, Error} , State}
>> end
>>
>> Regards,
>> Anton
>>
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>>
>
>


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