Whats the use of Nullable.GetUnderlyingType, if typeof(int?) is an Int32?

Question

why is typeof int? an Int32

int? x = 1;
Console.WriteLine(x.GetType().Name);

If it is okay then what\'s the use of

Answer 1

This example is a bit confused, because:

int? x = 1;

creates a Nullable like you expect; however:

Type tupe = x.GetType();

is a call to a non-virtual method on object, which isn't (and can't be) overridden - therefore this is a boxing operation; and Nullable has special boxing rules:

• if it is empty, it boxes to null
• if it has a value, the value is boxed and returned

i.e.

int? x = 1;
int y = 1;

box to exactly the same thing.

Therefore, you are passing typeof(int) to GetUnderlyingType.

A more illustrative example of when this helps is when using reflection:

class Foo {
    public int? Bar {get;set;}
}
...
Type type = typeof(Foo); // usually indirectly
foreach(var prop in type.GetProperties()) {
     Type propType = prop.PropertyType,
          nullType = Nullable.GetUnderlyingType(propType);

     if(nullType != null) {
         // special code for handling Nullable properties;
         // note nullType now holds the T
     } else {
         // code for handling other properties
     }
}