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Type Checking: typeof, GetType, or is?

ayi

<t>Type Checking: typeof, GetType, or is?</t>

ayi

<t>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 { } <br/>
class Dog : Animal { }<br/>
<br/>
void PrintTypes(Animal a) { <br/>
    Console.WriteLine(a.GetType() == typeof(Animal)); // false <br/>
    Console.WriteLine(a is Animal);                   // true <br/>
    Console.WriteLine(a.GetType() == typeof(Dog));    // true<br/>
    Console.WriteLine(a is Dog);                      // true <br/>
}<br/>
<br/>
Dog spot = new Dog(); <br/>
PrintTypes(spot);<br/>
<br/>
```<br/>
<br/>
  <br/>
What about `typeof(T)`? Is it also resolved at compile time?<br/>
<br/>
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:<br/>
<br/>
```<br/>
string Foo(T parameter) { return typeof(T).Name; }<br/>
<br/>
Animal probably_a_dog = new Dog();<br/>
Dog    definitely_a_dog = new Dog();<br/>
<br/>
Foo(probably_a_dog); // this calls Foo and returns "Animal"<br/>
Foo(probably_a_dog); // this is exactly the same as above<br/>
Foo(probably_a_dog); // !!! This will not compile. The parameter expects a Dog, you cannot pass in an Animal.<br/>
<br/>
Foo(definitely_a_dog); // this calls Foo and returns "Dog"<br/>
Foo(definitely_a_dog); // this is exactly the same as above.<br/>
Foo(definitely_a_dog); // this calls Foo and returns "Animal". <br/>
Foo((Animal)definitely_a_dog); // this does the same as above, returns "Animal"<br/>
<br/>
```</t>