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?

score 199 · Accepted Answer · edited Apr 27 '10 at 16:47

199

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

edited Apr 27 '10 at 16:47

Jon Skeet

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answered Apr 27 '10 at 16:39

LukeH

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score 46 · Answer 2 · edited May 23 '17 at 12:26

46

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;
}

edited May 23 '17 at 12:26

Community

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answered Apr 27 '10 at 16:35

Jon Skeet

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1

I think I'd have done it Luke's way; less complex for the caller. – Marc Gravell Apr 27 '10 at 16:44
2

@Marc: I don't see how it makes any odds for the *caller* - but Luke's way is certainly nicer than mine. – Jon Skeet Apr 27 '10 at 16:45
Yeah definitely keep it for future reference – adrin Apr 27 '10 at 16:50
Yeah. I would have done "public static bool IsNullableEnum(object value) { if (value == null) { return true; } Type t = value.GetType(); return /* same as Jon's return */ ; }" because it may work with boxed types. And then overloaded with LukeH answer for better performance. – TamusJRoyce May 02 '12 at 21:29

score 30 · Answer 3 · answered Apr 12 '16 at 13:28

30

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

answered Apr 12 '16 at 13:28

Bigjim

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score 1 · Answer 4 · answered Apr 27 '10 at 16:36

1

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.

answered Apr 27 '10 at 16:36

Bryan Watts

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score 1 · Answer 5 · answered Apr 27 '10 at 16:36

1

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

answered Apr 27 '10 at 16:36

Daniel Renshaw

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Checking if Type instance is a nullable enum in C#

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