MonoCecilExtensions

GetDeclaredTypeOfThisObject

Given an instance method call instruction this extension method return the declared type of the this object.

For example, consider the following code:

public interface IBase
{
    void f();
}

public interface IDerived : IBase
{
}

public class Derived : IDerived
{
    public void f(){}
}

...

void SomeFunction()
{
    IDerived obj = new Derived();
    obj.f();
}

Inspecting the function SomeFunction reveals that it depends on the method IBase.f, however, what does it mean in reality? IBase may have gazillion implementations. So the statement "SomeFunction depends on IBase.f" is not very helpful, if we want to figure out the dependencies of SomeFunction.

The crucial piece of dependency information here is that IBase.f is being called through a reference to the Derived object. However, I do not think it is possible in general to deduce it from the static code analysis. But, we can deduce the declared type of the object through which IBase.f is being called, i.e. the declared type of obj - IDerived.

This extension method does exactly that.

For details on how it works refer to the eponymous unit tests.

Generics

Right now the method depends on an external interface IGenericContext to resolve generic types in certain situations.

For example:

class SomeClass<TIntf, TImpl>
    where TIntf: IBase
    where TImpl: class, TIntf, new()
{
    void SomeFunction()
    {
        TIntf obj = new TImpl();
        obj.f();
    }
}

It seems impossible to deduce that TIntf is IDerived when SomeClass<IDerived, Derived> is used in code. This is because the MethodDefinition object corresponding to SomeClass<IDerived, Derived>.SomeFunction does not capture this information (as expected, since the single definition serves many generic instances). It seems the most we can obtain by inspecting the code of SomeFunction is that the declared type of obj is TIntf and to resolve it further we need some external help - enter the IGenericContext interface.

Credits

• This SO answer by Vagaus
• Referenced by the aforementioned SO answer - https://github.com/lytico/db4o/blob/master/db4o.net/Db4oTool/Db4oTool/Core/StackAnalyzer.cs