Checking if Type instance is a nullable enum in C#

Question

How do i check if a Type is a nullable enum in C# something like

Type t = GetMyType();
bool isEnum = t.IsEnum; //Type member
bool isNullableEnum = t.IsNullableEnum(); How to implement this extension method?

Answer 1

public static bool IsNullableEnum(this Type t)
{
    Type u = Nullable.GetUnderlyingType(t);
    return u != null && u.IsEnum;
}

Answer 2

EDIT: I'm going to leave this answer up as it will work, and it demonstrates a few calls that readers may not otherwise know about. However, Luke's answer is definitely nicer - go upvote it :)

You can do:

public static bool IsNullableEnum(this Type t)
{
    return t.IsGenericType &&
           t.GetGenericTypeDefinition() == typeof(Nullable<>) &&
           t.GetGenericArguments()[0].IsEnum;
}

Answer 3

As from C# 6.0 the accepted answer can be refactored as

Nullable.GetUnderlyingType(t)?.IsEnum == true

The == true is needed to convert bool? to bool

Answer 4

public static bool IsNullable(this Type type)
{
    return type.IsClass
        || (type.IsGeneric && type.GetGenericTypeDefinition == typeof(Nullable<>));
}

I left out the IsEnum check you already made, as that makes this method more general.

Answer 5

See http://msdn.microsoft.com/en-us/library/ms366789.aspx