[erlang-questions] Type specs depending on build-time selected code

Olivier BOUDEVILLE <>
Fri Nov 18 15:56:07 CET 2011


Hi,

I suppose there are situations where the actual code for a function is 
based on preprocessor defines while we want the type specs to encompass 
all possible implementations.

A simple example could be a debug mode which is to be enabled/disabled at 
build time:

"""
-module(foo).

-export( [is_debug_mode_enabled/0]).

 -spec is_debug_mode_enabled() -> boolean().

 -ifdef(debug_mode_is_enabled).

 is_debug_mode_enabled() ->
        true.

 -else.

 is_debug_mode_enabled() ->
        false.

-endif.
"""

(another example could be the use of a random source based on crypto - if 
available, otherwise on the built-in source)

Dialyzer is right when telling that "is_debug_mode_enabled/0 states that 
the function might also return 'false' but the inferred return is 'true'" 
(when the symbol debug_mode_is_enabled is defined) , but I would like to 
be able to suppress this warning as the same code built with a different 
preprocessor flag should offer the same API/type spec to the user code.

Of course I could define instead:

"""
 -ifdef(debug_mode_is_enabled).

-spec is_debug_mode_enabled() -> true.
 is_debug_mode_enabled() ->
        true.

 -else.

-spec is_debug_mode_enabled() -> false.
 is_debug_mode_enabled() ->
        false.

-endif.
"""

but then, I think it would not really solve the problem as I suppose that 
Dialyzer would similarly complain then in the user code relying on these 
functions, like in:

"""
-module(bar).
-spec f() -> boolean()
f() ->
        foo:is_debug_mode_enabled().
"""

(the problem would then be transferred from foo to bar and all other 
places making use of foo)

Am I missing something? Is there a way to tell Dialyzer to ignore *for 
this particular function* the "underspecification"? 
If not, maybe making Dialyzer support Valgrind-like suppression files 
could help?

Thanks in advance for any hint,
Best regards,

Olivier.
---------------------------
Olivier Boudeville

EDF R&D : 1, avenue du Général de Gaulle, 92140 Clamart, France
Département SINETICS, groupe ASICS (I2A), bureau B-226
Office : +33 1 47 65 59 58 / Mobile : +33 6 16 83 37 22 / Fax : +33 1 47 
65 27 13



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