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Getting more from your enumerations

Introduction

I had a situation come up where I needed to test whether a given value in a database fell inside the range of values given by an enumeration. After fussing around with several ways of testing this, I found a simple, elegant solution that seemed worth documenting.

The theory

In the .NET Framework, enumerations are handled by the Enum class. When you have a code such as

public enum SecurityLevel 
{
    Undefined = -1,
    Guest = 0,
    Assistant = 1,
    Representative = 2,
    Employee = 3,
    Executive = 5,
    Administrator = 8
}
VB.NET
Public Enum SecurityLevelEnum
    Undefined = -1
    Guest = 0
    Assistant = 1
    Representative = 2
    Employee = 3
    Executive = 5
    Administrator = 8
End Enum

the Framework actually creates an instance of Enum and populates it with your values. And like any class, Enum has methods that can be invoked.

The practice

Of interest is the Shared (static in C#) method GetValues, which takes the contents of an enumeration type and returns it as an instance of the System.Array class. If we take this result and convert it to an IEnumerable of a given type, we can use the LINQ extentions to get some useful information about the enumeration.

if ( ((int[]) Enum.GetValues(typeof(SecurityLevel))).Contains(7) )
...
if ( 3 >= ((int[]) Enum.GetValues(typeof(SecurityLevel))).Min() )
...
if ( 6 < ((int[]) Enum.GetValues(typeof(SecurityLevel))).Max() )
VB.NET
If CType([Enum].GetValues(SecurityLevel), Integer()).Contains(7) Then
...
If 3 >= CType([Enum].GetValues(SecurityLevel), Integer()).Min() Then
    ...
If 6 < CType([Enum].GetValues(SecurityLevel), Integer()).Max() Then

Note that because Enum is a keyword in VB.NET, using it as a class requires that you use square brackets.

The first example will return False, because the given enumeration does not contain a value that corresponds to the integer value 7. The second and third tests return True.

You can generalize this as a function which will work for any integer-based enumeration:

bool EnumHasValue(Type Typ, int Value)
{
    return ((int[])Enum.GetValues(Typ)).Contains(Value);
}

...
if (EnumHasValue(typeof(SecurityLevel), 7)
VB.NET
Function EnumHasValue(ByVal Typ As Type, ByVal Value As Integer) As Boolean
    Return CType([Enum].GetValues(Typ), Integer()).Contains(Value)
End Function
...
If EnumHasValue(GetType(SecurityLevel), 7) Then

Of course, enumerations do not have to be integer-based: you can convert the result of GetValues into an array of strings, doubles, whatever you can turn into an enumeration.

If your experimentation comes up with something interesting, please post your results as a comment.


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