Monday, October 23, 2006

Get first and last elements of an Enum

This article applies to C# 2.0

From time to time (not very often) we have an enumeration and we want certain parameter (perhaps coming from a db) to be within the bounds of our enumeration (remember that it's legal to cast any integer value into an Enum, even if the value is out of the range defined in your Enum), most of the code I have seen just checks if such value is less than the last element in the enum, something like:

enum TestEnum {

  Enum1 = 1, Enum2 = 2, Enum3 = 3;


TestEnum myValue; //this might be coming as a parameter to a function

if (myValue > TestEnum.Enum3) //some code to handle this situation

and each time you have to update the enumeration, you have to take care of changing this part of the code.

This function returns the first and last elements (not int values) of an Enum, I wrote it using generics so you can reuse it with any Enum type, you could modify this to be specific to your enum and the function could be used in C# 1.0 (VS2003), the use of the function is probably rare, but anyway, here it is

public void GetLowHighFromEnum<T>(out T lowElement, out T highElement) {
if (!typeof(T).IsSubclassOf(typeof(Enum))) //make sure we got an Enum
throw new ArgumentException("parameterized type should be Enum");
T[] values = (T[])Enum.GetValues(typeof(T));
lowElement = values[0];
highElement = values[values.Length - 1];

To use it, it would be something like:

TestEnum te1, te2;
GetLowHighFromEnum<TestEnum>(out te1, out te2);

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