C#, Flags Enum, Generic function to look for a flag

Question

I'd like one general purpose function that could be used with any Flags style enum to see if a flag exists.

This doesn't compile, but if anyone has a suggestion, I'd appreciate it.

public static Boolean IsEnumFlagPresent<T>(T value,T lookingForFlag) 
       where T:enum
{
    Boolean result = ((value & lookingForFlag) == lookingForFlag);
    return result ;            
}

Answer 1

No, you can't do this with C# generics. However, you could do:

public static bool IsEnumFlagPresent<T>(T value, T lookingForFlag) 
    where T : struct
{
    int intValue = (int) (object) value;
    int intLookingForFlag = (int) (object) lookingForFlag;
    return ((intValue & intLookingForFlag) == intLookingForFlag);
}

This will only work for enums which have an underlying type of int, and it's somewhat inefficient because it boxes the value... but it should work.

You may want to add an execution type check that T is actually an enum type (e.g. typeof(T).BaseType == typeof(Enum))

Here's a complete program demonstrating it working:

using System;

[Flags]
enum Foo
{
    A = 1,
    B = 2,
    C = 4,
    D = 8
}

class Test
{
    public static Boolean IsEnumFlagPresent<T>(T value, T lookingForFlag) 
        where T : struct
    {
        int intValue = (int) (object) value;
        int intLookingForFlag = (int) (object) lookingForFlag;
        return ((intValue & intLookingForFlag) == intLookingForFlag);
    }

    static void Main()
    {
        Console.WriteLine(IsEnumFlagPresent(Foo.B | Foo.C, Foo.A));
        Console.WriteLine(IsEnumFlagPresent(Foo.B | Foo.C, Foo.B));
        Console.WriteLine(IsEnumFlagPresent(Foo.B | Foo.C, Foo.C));
        Console.WriteLine(IsEnumFlagPresent(Foo.B | Foo.C, Foo.D));
    }
}