Add code to automatically generated class in SWIG

Question

I'm trying to find a way to add code to swig generated functions. I have used typemaps to extend classes, but can't find anything in the documentation about extending specific functions.

Given the following swig interface file:

%module Test
%{
#include "example.h"
%}

%typemap(cscode) Example %{
    bool 64bit = SizeOf(typeof(System.IntPtr)) == 8;
    static string Path = 64bit ? "/...Path to 64 bit dll.../" : 
                                 "/...Path to 32 bit dll.../";
%}

%include "example.h"

I get the following C# code:

public class MyClass : global::System.IDisposable {
    ...
    bool 64bit = SizeOf(typeof(System.IntPtr)) == 8;
    static string Path = 64bit ? "/...Path to 64 bit dll.../" : 
                                 "/...Path to 32 bit dll.../";

    ...
    public static SomeObject Process(...) {     // Function defined in example.h
                                               <- I would like to add some code here.
        SomeObject ret = new SomeObject(...);

    }
    ...
}

I would like to add some code to the function Process, this code is a call to SetDllDirectory(Path) which loads the correct dll depending on the platform type. This needs to happen inside the Process() call.

Any help is greatly appreciated!

Isaac

Never having used swig (and based on what I just googled) it seems that you want to inject C# specific code (SetDllDirectory()) during the translation from the preexisting C++ source file. If that is right, then I think you have to rearrange your C++ code to accommodate that injection. EG Creating a stub virtual function call in Process() C++ code which you can later override once you are in the C# realm. – Wynn

possible duplicate of Is it possible to add code to an existing method when using Swig to build a C# wrapper for C++ code? – Attainable

@PeterM That's the sort of approach I was thinking of, but couldn't find a way to actually make it work. Flexo has given an alternative way to inject C# code directly which I'll try out. – Isaac

Answer 1

You can generate the code you're looking for using %typemap(csout). It's a bit of a hack though, and you'll need to copy some of the existing typemap for SWIGTYPE (which is a generic place holder) that can be found in csharp.swg

So for example, given a header file example.h:

struct SomeObject {};

struct MyClass {
  static SomeObject test();
};

You can then write the following SWIG interface file:

%module Test
%{
#include "example.h"
%}

%typemap(csout,excode=SWIGEXCODE) SomeObject {
    // Some extra stuff here
    $&csclassname ret = new $&csclassname($imcall, true);$excode
    return ret;
}

%include "example.h"

Which produces:

public static SomeObject test() {
    // Some extra stuff here
    SomeObject ret = new SomeObject(TestPINVOKE.MyClass_test(), true);
    return ret;
}

If you want to generate that for all return types, not just things which return SomeObject you'll have a bit more work to do for all the variants of csout.

Annular

This looks great, thanks. I'll give it a go and see if I can get a working version together. – Isaac

Answer 2

Section 20.8.7 of the SWIG docs shows how to use typemap(cscode) to extend generated classes.

Hartsell

That allows you to add extra methods, but not extend an existing method. – Isaac

I believe I saw a post that uses cscode with %ignore and %rename but I cant find it now... – Hartsell