Question

On a few separate occasions, I have tried to coax the declared type out of a variable, relatively far from its declaration, only to find out that typeof(T) only works on type names.

I was wondering if there would be any breaking changes to allow typeof(variable) as well.

For example, with this code:

class Animal { /* ... */ }
class Goat : Animal { /* ... */ }

/* ... */

var g = new Goat();
Animal a = g;

Console.WriteLine(typeof(Goat));
Console.WriteLine(typeof(Animal));
Console.WriteLine(g.GetType());
Console.WriteLine(a.GetType());

You get something like:

Goat
Animal
Goat
Goat

Why is it not possible to do this:

Console.WriteLine(typeof(g));
Console.WriteLine(typeof(a));

Goat
Animal

I have given the spec a cursory glance, and can’t find any conflict. I think that it would clear up the question ‘Why this type?’ when using the typeof operator.

I know that the compiler is capable, here. An implementation using extension methods is actually trivial:

public static Type TypeOf<T>(this T variable)
{
    return typeof(T);
}

But that feels dirty, abusing the type-inference of the compiler.

Answer 1

Suppose it’s allowed:

class Animal { }

string Animal;
Type t = typeof(Animal); // uh-oh!