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Type Checking: typeof, GetType, or is?

Submitted by: @import:stackoverflow-api·Mar 10, 2026·

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gettypetypetypeofchecking

Problem

I've seen many people use the following code:

Type t = typeof(SomeType);
if (t == typeof(int))
    // Some code here

But I know you could also do this:

if (obj1.GetType() == typeof(int))
    // Some code here

Or this:

if (obj1 is int)
    // Some code here

Personally, I feel the last one is the cleanest, but is there something I'm missing? Which one is the best to use, or is it personal preference?

Solution

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"

Code Snippets

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);

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

Context

Stack Overflow Q#983030, score: 2309

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