Is there a pattern or a method in C# to check if an (int 1,2,4,8,...) option is true or false

Question

I like to write enum or integer to pass option to my methods. Is there a pattern or a method in C# to check if an (int 1,2,4,8,...) option is true or false. I think it should easily be possible via binary functions.

class Program
{
    public enum Option
    {
        Option_A = 1,
        Option_B = 2,
        Option_C = 4,
        Option_D = 8,
    }

    static void Main(string[] args)
    {
        int activeOption = 5; // Means I activeted the Option_A and Option_C
        if (IsOption(activeOption, Option.Option_A)) { /*do work*/ }
        if (IsOption(activeOption, Option.Option_B)) { /*do work*/ }
        if (IsOption(activeOption, Option.Option_C)) { /*do work*/ }
        if (IsOption(activeOption, Option.Option_D)) { /*do work*/ }
    }

    private static bool IsOption(int activeOption, Option option)
    {
        /*Evaluate if IsOption is true or false*/
        throw new NotImplementedException();
    }
}

EDIT

Am I limited the number of options that I can create like this?

Answer 1

Use bitwise AND to check if the bits in option are set in activeOption. You also need to make both parameters the same type so the operator will work (you are checking the bits in an Option bitmask anyway):

private static bool IsOption(Option activeOption, Option option)
{
    return (activeOption & option) == option;
}

Answer 2

Since your enum contains flags (or if you prefer, is a bitfield), you should add a FlagsAttribute to it:

[Flags]
public enum Option
{
    Option_A = 1,
    Option_B = 2,
    Option_C = 4,
    Option_D = 8,
}

And then, checking is typically done with the bitwise and operator. A cast will also be needed, because you are using an int variable.

if(((Option)activeOption & Option.Option_A) != Option.Option_A) //...

If you want to encapsulate this nastiness away, check out the article linked in Smudge202's answer. If you are running .NET 4, you don't even need to do that: check sehe's answer.

But you should really try using a variable of type Option directly, and combine the options with the bitwise or operator:

Option activeOption = Option.Option_A | Option.Option_C;

Of course using this scheme limits the number of options you can create. If you leave it as is, you can only create 32 different options, because an int (the default underlying type of an enum) has only 32-bits. If you use a long you can have 64 different options:

[Flags]
public enum Option : long
{
    Option_A = 1,
    Option_B = 2,
    Option_C = 4,
    Option_D = 8,
    // blah blah
}

However, if you need an arbitrary number of options, it's probably time to change strategies. You could make a custom type that behaves like an enum, but you'll probably be better off with just a regular, non-flags enum, and a HashSet<Option>.

public enum Option
{
    Option_A = 1, // notice the sequential values now
    Option_B = 2,
    Option_C = 3,
    Option_D = 4,
}

HashSet<Option> options = new HashSet<Option> { Option.Option_A, Option.Option_C };
if(options.Contains(Option.Option_A)) // ...