Question

I was wondering if it was possible to dynamically inject a function parameter at runtime. For e.g. I have a class with two overloaded methods say

Class C1
{
    public static void Func1(object o)
    {
    }

    public static void Func1()
    {
    }       
}

Class C2
{

    public void Func1()
    {
       C1.Func1();
    }
}

Now, is it possible to dynamically replace the call to Func1() with a call to the overloaded method C1.Func1(object o) passing in either ‘this’ or the type object as the parameter.

So, in affect when I call C1.Func1(), my code should call C1.Func1(this);

Answer 1

I am assuming that by “dynamic” you mean a post-compile time solution, but not necessarily at runtime. The latter would be more challenging but could be done. For the former it’s rather easy if you know some IL. I note that C2.Func1 compiles to something like

.method public hidebysig instance void Func1() cil managed {
    call void SomeNamespace.C1::Func1() 
    ret 
}

which you can easily replace with

.method public hidebysig instance void Func1() cil managed {
    ldarg.0
    call void SomeNamespace.C1::Func1(object)
    ret 
}

This is because argument zero in an instance method is always the this reference for the current instance and we can push it on the stack with the instruction ldarg.0. Moreover, we simply replace the signature of the method that we are invoking from the parameterless method to the method accepting a single object as a parameter.

You can easily decompile to IL using ildasm and recompile using ilasm.