[erlang-questions] How about a new warning? Was: Re: trouble with erlang or erlang is a ghetto

Kenneth Lundin <>
Wed Aug 17 22:09:23 CEST 2011


I agree that it is very common in test code to match against already bound
variables.
But in production code it is quite rare.
The warning should definitely not be on by default.
We will also run a check over all OTP libraries and possibly other
production code
as well to see how it turns out before we make any definite decisions.

But as said we have not given the implementation any priority at all yet.

/Kenneth

2011/8/17 Steve Vinoski <>:
> 2011/8/3 Frédéric Trottier-Hébert <>:
>> On 2011-08-02, at 01:59 AM, Richard O'Keefe wrote:
>>
>>> 2. Is matching against an already-bound variable a check we want?
>>
>> To me, matching against an already-bound variable is is a valid
assertion, as much as 'ok = function_call()' might be, and as implicit as
'{ok, Pid}' or '{error, already_started}' might be. Matching on
already-bound variables is part of my standard code when trying to crash
early when possible, and also part of many basic test suites that simply do
pattern matching here and there. To me it's as basic as using the same
variable twice in a single pattern (f([A,A,B,B|_]) when A =/= B -> ...), or
something similar with records.
>>
>> I would likely not use the check at all, and if it were to be added,
would prefer it to be a compiler argument (which could be enabled in
-compile(...).) I foresee little use of such warnings for myself and would
dislike to see it becoming a default setting.
>
> I completely agree. I use matching this way quite a bit, especially in
> testing, and wouldn't want to see any warnings for it by default.
>
> --steve
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