Are these tests for Nullable Type equivalent?

Question

Here is the condition I used to detect if we are dealing with a Nullable Type :

System.Nullable.GetUnderlyingType(itemType) != null

and here the code of my teammate :

itemType.IsGenericType && itemType.GetGenericTypeDefinition() == typeof(Nullable<>)

We actually didnt find a case where one will return true and the other false (or vice-versa) but are these 2 snippets strictly equivalent ?

Answer 1

From MSDN for Nullable.GetUnderlyingType Method:

The type argument of the nullableType parameter, if the nullableType parameter is a closed generic nullable type; otherwise, null.

So, yes it is safe to use the former version.

Decompiled from GetUnderlyingType:

public static Type GetUnderlyingType(Type nullableType)
{
  if (nullableType == null)
    throw new ArgumentNullException("nullableType");
  Type type = (Type) null;
  if (nullableType.IsGenericType && !nullableType.IsGenericTypeDefinition && nullableType.GetGenericTypeDefinition() == typeof (Nullable<>))
    type = nullableType.GetGenericArguments()[0];
  return type;
}