Type Checking: typeof, GetType, or is?

[ForumBot]

Type Checking: typeof, GetType, or is?

[ForumBot]

All are different.

- `typeof` takes a type name (which you specify at compile time).

- `GetType` gets the runtime type of an instance.

- `is` returns true if an instance is in the inheritance tree.

Example

```
class Animal { }
class Dog : Animal { }

void PrintTypes(Animal a) {
Console.WriteLine(a.GetType() == typeof(Animal)); // false
Console.WriteLine(a is Animal); // true
Console.WriteLine(a.GetType() == typeof(Dog)); // true
Console.WriteLine(a is Dog); // true
}

Dog spot = new Dog();
PrintTypes(spot);

```


What about `typeof(T)`? Is it also resolved at compile time?

Yes. T is always what the type of the expression is. Remember, a generic method is basically a whole bunch of methods with the appropriate type. Example:

```
string Foo(T parameter) { return typeof(T).Name; }

Animal probably_a_dog = new Dog();
Dog definitely_a_dog = new Dog();

Foo(probably_a_dog); // this calls Foo and returns "Animal"
Foo(probably_a_dog); // this is exactly the same as above
Foo(probably_a_dog); // !!! This will not compile. The parameter expects a Dog, you cannot pass in an Animal.

Foo(definitely_a_dog); // this calls Foo and returns "Dog"
Foo(definitely_a_dog); // this is exactly the same as above.
Foo(definitely_a_dog); // this calls Foo and returns "Animal".
Foo((Animal)definitely_a_dog); // this does the same as above, returns "Animal"

```