How to write an operator in VB-style?

[Physicus]

Hi,

is there any possibility to write an operator member function for a ref class in C++/CLI which can be called directly from Visual Basic using the common Visual Basic syntax? Of course this can be done with an additional (VB-)wrapper class - but without?

In detail:
Assume we have a ref class written in C++/CLI, let's call it MyClass.
In MyClass we have a member function: static bool operator==(const MyClass^ left, const MyClass^ right).
Now, we make a dll of this project and import it into a VB-programm. Then we can call this operator function from within VB using the following syntax: MyClass.op_Equality(Left, Right) where Left and Right are objects of type MyClass.
But this it not VB-style syntax.

Of course we can declare a wrapper class, e.g. VBClass with an operator function:
Public Shared Shadows Operator =(ByVal Left As VBClass, ByVal Right As VBClass) As Boolean
in which we call .op_Equality(). Then we can use this wrapper class and call the operator function in VB-syntax style (e.g. If Obj1 == Obj2 Then ...).

BUT: I don't want to have an additional wrapper class (in my project I already have 3 nested wrapper classes and I don't want to have a fourth one!).

THEREFORE: Is there any possibility to write an operator member function within C++/CLI in such a way it will be understood from within VB (with it's syntax)?


Many thanks in advance,

Physicus.

[Eri523]

You may try to define an operator like the one you want in VB, e.g.

Public Shared Shadows Operator =(ByVal Left As VBClass, ByVal Right As VBClass) As Boolean

and then use ILDasm to see what signature VB has generated for the operator definition. Once you know that you can try to mimic it in C++/CLI.

For instance, the signature generated by C++/CLI for

static bool operator==(const MyClass ^left, const MyClass ^right)

is

.method assembly static bool 
        marshal( unsigned int8) 
        '?A0xb221482d.=='(class MyClass modopt([mscorlib]System.Runtime.CompilerServices.IsConst) left,
                          class MyClass modopt([mscorlib]System.Runtime.CompilerServices.IsConst) right) cil managed

. But as you said, this one can't be called as an operator from VB. (Hint: It would probably have been easier to find if it was a MyClass member instead of a free function.)

There may be, however, a much easier way to achieve your goal that I don't know of because I know close to nothing about VB.NET.

HTH

[Alex F]

With MyClass.op_Equality (operator==) method, when you write Left = Right in VB program, does VB call this operator or just compares references? Looking at String.op_Equality Method http://msdn.microsoft.com/en-us/libr...s.80).aspx#Y15, I see that string class just defines operator==, and this is enough for VB and C# compilers to convert = to this operator call.

[Physicus]

@Alex:

wow!!! You are quite right - it works!
The reason why I didn't find out this was: I first wrote the operator functions in C++/CLI as object member functions (not static). VB couldn't access them. Later I formulated the member functions as static functions - but then I didn't tried not any longer to use them directly like you suggested.

Thank you very much! Problem is solved!


Best regards,

Physicus.

[Eri523]

Wow! I considered the operator might be a non-static class member (in that case with only one parameter) or a free function (in which case it actually shouldn't be static if it is to be called from another module, on second thought)... but not a static class member, a variant that I've never seen for an operator like this in native C++. (And apparently it doesn't work there anyway; just quick-checked it.)