Re: [Swig-user] Template class, typemap not applied!

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

Steven N. Hirsch wrote:
> On Sat, 4 Nov 2006, William S Fulton wrote:
> 
>> There aren't many perl experts around on the list. Nevertheless, I don't
>> see what the problem is. I tried this interface file:
>>
>> // File: example.i
>> %module example
>>
>> %inline %{
>> #include <iostream>
>> using namespace std;
>> template <class T>
>> class foo_base {
>> public: // must be public
>>   void bar( T parm1 ) {
>>     cout << parm1 << endl;
>>   }
>> };
>> %}
>> %template(foo_char) foo_base<char *>;
>>
>> %inline %{
>> class foo_derived : public foo_base<char *> {
>> //  ....
>> };
>> %}
>>
>> with this:
>>
>> # file: runme.pl
>> use example;
>>
>> $fd = new example::foo_derived();
>> $fd->bar( "Hello, world" );
>>
>> Run through swig-1.3.30rc1 and the output is:
>>
>> $ perl runme.pl
>> Hello, world
>> $
>>
> 
> Yes, that exact syntax DOES work.  However, you will see the problem if 
> you change the declaration of foo_base::bar to:
> 
> void bar( const T & parm1 );
> 
> or
> 
> void bar( T & parm1 );
> 
> 
> In either case, you will then have to explicitly define this in 
> class foo_derived:
> 
> ....
> 
> public:
>     int bar( char *arg1 ) {
>         return foo_base<char *>::bar( arg1 );
>     }
> 
> .....
> 
> in order to have Swig generate workable code.
> 
Yes, this is a bug. Please put it in the bug tracker.

> Also, I would have thought it possible to use the %extend pragma to define 
> the explicit overload, but it does not work.  For example, instead of 
> placing the overloaded 'bar' method inside foo_derived (as above), I 
> tried:
> 
> %extend foo_derived {
> 
>     int bar( char *arg1 ) {
>         return foo_base<char *>::bar( arg1 );
>     }
> 
> };
> 
> It fails at compile time with a complaint of
> 
> ".. cannot call member function foo_base<T>::bar(const T&) without object"
> 
> I've read and re-read the documentation for extend until my head hurt, and 
> it appears as if this should work.  For whatever reason, Swig cannot 
> understand that I'm adding a class method.
> 
Okay, so this isn't clearly documented and I'll fix that up, but you need:

   return self->foo_base<char *>::bar( arg1 );

instead of

   return foo_base<char *>::bar( arg1 );

self is equivalent to the 'this' pointer. You can't use 'this' as the
%extend method is actually a global function, take a look at the
generated code.

William