[Mono-list] how to "register" a c++ class to c#?

Christopher David Howie me at chrishowie.com
Mon Jun 7 11:17:22 EDT 2010

On 06/07/2010 10:19 AM, 冶晶邓 wrote:
> thanks,Jedd!
> i think i have understood the code  you supplied.
> i wonder if we can create a C# class with some C-API instead of directly
> defining it in C#? just like python who enables us to create new type by
> filling a PyType struct and pass it to PyType_Ready call.
> is that exists?

You technically do have this capability, but this would not be very
helpful to people who want to code against this class.  Since C# is at
heart a static language, it needs to know how types are defined in
advance for other developers to make use of them.

However, you can define a public *interface* in an assembly, and then
emit a completely new class that implements this interface at runtime.
This is a very common technique when writing bindings for remoting
protocols in .NET; the bindings let the user define an interface that
also defines the RPC interface they want to use, then the bindings
implement that interface on a transparent proxying class
behind-the-scenes.  The user only needs to know about the interface type
in advance, not the implementation.

So, for example, if your class has "public: void foo(); void bar();"
then you could define in an assembly:

public ISomeClass
    void Foo();
    void Bar();

Then you can emit a new class at runtime that will effectively be:

class SomeClass : ISomeClass
    private delegate void FooCallback();
    private delegate void BarCallback();

    private FooCallback fooCallback;
    private BarCallback barCallback;

    public SomeClass(FooCallback fooCallback, BarCallback barCallback)
        this.fooCallback = fooCallback;
        this.barCallback = barCallback;

    public void Foo()

    public void Bar()

This approach has the strong advantage that you are free to reimplement
this interface a different way in the future if your internal binding
needs to change.

Note that I'm not terribly familiar with libmono, so I won't be able to
provide the calls required to emit this class and to obtain and call the
constructor.  (Were it 100% C# I would...)  Perhaps someone else can
chime in with that info.

Chris Howie

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