[Swig-user] Re: C# references, %extend and %typemaps

[Clinton C. <cl...@cl...>]

>I am running into a problem where an object whose class is wrapped by SWIG,
> is referenced in C#, and then gets garbage collected because it is
> apparently no longer used. In reality, it is used by some C code, to which
> is passed the aforementioned C# reference. 
>
> I am trying to apply section 17.4.2 of the SWIG Manual, which explains
that
> I should create another reference to the object, to be stored as a member
> variable of the C# proxy class. 

[...]   
 
> Unfortunately, it doesn't seem like %typemaps can be applied to code that
is
> generated from an %extend, probably because the %extend code is generated
> after all %typemaps have been applied.
 
Doh! I can't believe I missed section 10.2.2:

--->8--
One exception to the typemap scoping rules pertains to the %extend
declaration. %extend is used to attach new declarations to a class or
structure definition. Because of this, all of the declarations in an %extend
block are subject to the typemap rules that are in effect at the point where
the class itself is defined. For example:

class Foo {
   ...
};

%typemap(in) int {
 ...
}

%extend Foo {
   int blah(int x);    // typemap has no effect.  Declaration is attached to
Foo which 
                       // appears before the %typemap declaration.
};
---8<--

All I had to do was make sure that my %typemap occurs before my definition
of the structure.

---
Grace makes beauty out of old dead things. [U2]