Re: Howto override the argument names of certain class member functions

Hi Terry


On Sat, 27 Jun 2020 at 10:42, Terry Barnaby <[email protected]> wrote:

> Hi William,
>
> I have a large class library. There are multiple functions that have a,
> say, "(Channel& chan)" argument. In most cases these are used to return
> values, but in some cases the functions modify the contents of the object
> who's reference is passed. So I cannot generically use the %template
>

I think you meant %apply.

system as that only applies to the type and names of arguments passes,
> there is not ability to say a particular function is just using that
> argument as an output return. A lot of this libraries code is auto
> generated from a IDL and I generate a set of modified *.h files with the
> argument names changed to OUTPUT at the appropriate places but quite a few
> class member functions are not like that.
>
So I think you are saying you want to %apply these typemaps for parameters
with the same name and type, but only on a select few functions and you
don't want to modify the header files. The best solution SWIG has is to use
%apply and %clear as Rui alluded to. This will work to some degree as the
%apply will apply for all the functions in a header file you have include
with %include. You can then use %clear after the %include. If you want to
selectively apply the typemaps to parameters with the same type and name in
one header file, then the next best solution is to use %ignore and then add
the functions back in with %extend, renaming the parameters to something
else. You imply that you only have a few of these that you don't want the
typemaps to apply to, so this might be workable for you.

Looking at the original post, you have this in a header file:

  class DataFile {
   public:
       Error setInfo(const Info& info);    // Input only reference
       Error getInfo(Info& info);        // Output only reference
   };

the types are NOT the same as one is const and the other is not const. If
you look at the typemap rules, you'll see that if you have a typemap for
const Info&, it will not apply to non-const Info&. However a non-const
Info& typemap it wil apply to const Info&. So if you want to consistently
apply typemaps to const and non-const, then solution is easy, something
like:

%typemap(argout) const Info& OUTPUT "" // does nothing (effectively clears
the typemap)
%typemap(argout) Info& OUTPUT "/* some code for argout*/"
%apply Info& OUTPUT { Info& info };
%apply const Info& OUTPUT { const Info& info };

The main reason SWIG does not have function and parameter name combinations
for typemaps is there is no C++ scoping syntax to get at the scope of a
parameter name from outside of the function. I can elaborate more if anyone
is really interested.

William



> Terry
> On 27/06/2020 10:05, William S Fulton wrote:
>
> Hi Terry
>
> The %apply that Rui mentioned just applies the typemap you want for these
> named arguments and types. You can use these %apply directives before SWIG
> parses your unmodified C++ header files containing the original argument
> names. I don't see a reason to modify your header files, can you elaborate
> why you think you need to do that?
>
> William
>
> On Tue, 23 Jun 2020 at 06:19, Terry Barnaby <[email protected]> wrote:
>
>> Many thanks for your reply, yes I could do something like that but this
>> is a complex library with lots of classes and functions defined in
>> header files and I wanted to leave those header files alone and get SWIG
>> to use them directly. I don't want to rewrite the header files into SWIG
>> definition files as that would be a lot of work and unmaintainable. So I
>> was hoping that SWIG could, somehow, apply an argument rename on a
>> function by function basis.
>>
>> I have done it at the moment by pre-processing all of the header files
>> through sed before SWIG sees them, but that's a bit messy.
>>
>> Terry
>> On 22/06/2020 10:54, Rui Oliveira wrote:
>> > Hey,
>> >
>> > You're probably looking to do something like:
>> >
>> > %apply (float complex *OUTPUT) {(liquid_float_complex *_y),
>> > (liquid_float_complex *_x_hat)};
>> > void modem_modulate(modem _q, unsigned int _s, liquid_float_complex
>> *_y);
>> > void modem_get_demodulator_sample(modem _q, liquid_float_complex
>> > *_x_hat);
>> > %clear (liquid_float_complex *_y), (liquid_float_complex *_x_hat);
>> >
>> > This is an example from code I've written. This is documented in:
>> > http://www.swig.org/Doc4.0/SWIGDocumentation.html#Arguments_nn7
>> >
>> > Basically you write typemaps with generic names and then apply them to
>> > your particular function arguments.
>> > Me personally, I like to clear %apply directives when I no longer need
>> > them to avoid bugs to do "stray" typemaps.
>> >
>> > Hope it helped.
>> >
>> > Às 10:46 de 22/06/2020, Terry Barnaby escreveu:
>> >> I am wrapping a relatively complex C++ class library to produce a
>> >> Python interface. One thing I haven't worked out how to do is to tell
>> >> SWIG to return certain function reference arguments on the lhs of the
>> >> function call only, ie. assume them to be OUTPUT only references. For
>> >> example (very simplified):
>> >>
>> >> class DataFile {
>> >>
>> >> public:
>> >>
>> >>     Error setInfo(const Info& info);    // Input only reference
>> >>
>> >>     Error getInfo(Info& info);        // Output only reference
>> >>
>> >> };
>> >>
>> >> Now I can rename the getInfo function in the C++ class library to
>> >> "Error getInfo(Info& OUTPUT);" say and add the appropriate typemaps
>> >> to match this and that works, but I really don't want to rename all
>> >> of the C++'s API function arguments for all of the classes in this
>> >> library (They are used for doxygen etc).
>> >>
>> >> This there a simple way in SWIG to override/rename the arguments of a
>> >> particular function and/or particular classes member function ? So
>> >> something like:
>> >>
>> >> %rename("getInfo(Info& OUTPUT)") "getInfo(Info& info)"
>> >>
>> >> %rename("DataFile::getInfo(Info& OUTPUT)") "DataFile::getInfo(Info&
>> >> info)"
>> >>
>> >>
>> >>
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>> >
>> >
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>>
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>

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