c# - Casting to Generic base class failing

Question

I am failing to see why my attempt to cast to a generic base class is not working.

The basic structure of the code is as follows.

interface ICmd
{
}

class Context
{
}

class Cmd<TContext> : ICmd
    where TContext : Context
{
}

class MyContext : Context
{
}

class MyCmd : Cmd<MyContext>
{
}

So now I have an instance of ICmd and want to cast it to Cmd as follows

var base = cmd as Cmd<Context>

base is always null after this line is executed.

changing cast to be specific for the context only and it works.

var base = cmd as Cmd<MyContext>       -- this works ???

Hope I have provided enough information, is this a covariancecontravariance issue?

Thanks

Answer 1

You may want to use co- and contravariance.

The problem is that Cmd<Context> is not the base class of Cmd<MyContext>.

See this recent question for a more detailed answer: C# Generics Inheritance Problem