Re: [Swig-user] Typemap pattern matching question

[William S F. <ws...@fu...>]

Leo Breebaart wrote:
> I am currently stuck trying to SWIGify a library, but I'm fairly
> sure that my problem is unfamiliarity with the SWIG way of doing
> things, rather than anything else.
> 
> I have two different functions:
> 
>   foo(int x, double *dst);
>   bar(int x, double *dst, int y);
> 
> In foo(), 'dst' is a scalar output parameter. In bar(), it is an
> array output parameter (to be pre-allocated by the user).
> 
> My problem is simply: how can I tell SWIG to differentiate
> between the two, and not generate the same code in both cases?
> 
> If I do:
> 
>    (1)  %apply double *OUTPUT { double *dst };
> 
> I get the scalar code in both cases, which is wrong for 'bar'. If
> I do:
> 
>    (2)  %apply double[] { double *dst };
> 
> I get the array code in both cases, which will actually also work
> in the scalar case -- but it just seems so wasteful and
> inelegant.
> 
> If I try something like:
> 
>    (3)  %apply double[] { (int x, double *dst, int y) };
> 
> in an attempt to use the pattern matching algorithm to get SWIG
> to apply the array typemap only to bar(), I get a SWIG "Number of
> arguments don't match" error.
> 
The double[] typemap has not been written for multiple arguments, so 
this won't work. You'd have to write your own multiple argument typemap 
for this to work.

> Finally, there's (I think):
> 
>    (4) change the name of the parameter to *dst_array in the bar
>    signature
> 
> It is difficult for me to do that because I am not the person
> controlling the library in question. Also, I am simply curious by
> now to learn what the experts would do in the situation where (4)
> is not an option.
> 
> So my question: should I just stick with (2), or is there a more
> natural / preferred SWIG way of solving what I am trying to do
> here?
> 
> If it helps, my target language is Java, and the double[] typemap
> in question is defined in the system's "array_java.i" file.
> 
> I will be very grateful for any kind of feedback on this issue!
> 

Add the declaration of bar into your interface file, then ignore any 
subsequent versions (ie the one that will be in the header being wrapped)...

%apply double *OUTPUT { double *dst };

void bar(int x, double *dst_array, int y);
%ignore bar(int x, double *dst, int y);

or if bar and foo are in different headers, use the preprocessor to 
change dst for one of them

%include "foo.h" // asumming foo is declared in foo.h
#define dst dst_array
%include "bar.h" // assuming bar is declared in bar.h

William