[Swig-devel] C#: Patch to allow overloading operator==

[Olly B. <ol...@su...>]

In C#, the default == test for objects just tests if two object
reference refer to the same object instance.  That's useless if
you're wrapping C++ iterator classes (since the equality test
with the end iterator will always be false and any loops will
never end!)

So I want to overload operator== in C#, via SWIG.  I'm using
Mono C# 1.1.8.0, should that matter.

I've attached simpleitor.i which I've been using to try to get this to
work.  This wraps a C++ class "I" which represents an iterator over the
integers modulo 5.  So i == i + 5 (except I've not implemented
operator+).

As well as operator==, I've overloaded operator!= (because the compiler
insists), and also Equals and GetHashCode (I get warnings if I don't).
I realise my GetHashCode implementation is rather primitive...

I'm testing with Test.cs (also attached).

But I get a null dereference if I run the example.  I've no idea how
to run a debugger on C#, but it appears that the problem is that SWIG
generated code implicitly called from my operator== tests "obj == null"
where obj is an instance of class I, so my overloaded == is being
invoked.  If I change this to "(object)obj == null", then I avoid the
recursion and my test works.

I'm not completely sure I've diagnosed the problem correctly, but the
patch does seem to fix it.  Thoughts?

Cheers,
    Olly