Multi interface type declarations

[IAmTheCShark]

First of all, I have a hardtime naming / wording this, so if this has allready been proposed, im sorry for that.

Imagine you have this Method

public void DoSomething<T>(T arg) where T: IFoo, IBar {...}

Now think about what it means if you want to use a mock to test this method.
How do you provide this T argument when writing that unittest using a Mock?
It's a mess.

Second example, different usecase

Some reflectioncode needs to know if some object is both IFoo and IBar

if(obi is IFoo foo && obj is IBar bar) { }

you have essentially two variables, but how do you call that DoSomethingMethod from earlier?.

Proposal to solve this issue:

Create a way to define/construct/declare types like generic types.

declare TFooBar : IFoo, IBar;  

define TFooBar : IFoo, IBar;

using TFooBar : IFoo, IBar; 

var mock = new Mock<TFooBar>();
mock.Setup(f => f.FooProperty).Returns(7);
mock.Setup(f => f.BarProperty).Returns(8);
Whatever.DoSomething(mock.Obj);

if(obj is TFooBar  fooBar) {
    Whatever.DoSomething(foobar);
}

[IAmTheCShark]

Nevermind i found it right after I started this discussion :(
#399