Combining Enum Values with Bit-Flags

Question

I have this scenario where user has its role

NormalUser
Custodian
Finance

both Custodian and Finance is a Super

Answer 1

I think this might be a duplicate of How do you pass multiple enum values in C#?

Where the & bitmask can do the trick.

((Role.NormalUser & Role.All) == Role.NormalUser)

Inspecting this closer you will get the following:

0b0 & 0b11 == 0b0

However if you lets say want to check if the SuperUser is in finance you will get the following:

((Role.SuperUser & Role.Finance) == Role.Finance)

This will evaluate to:

0b11 & 0b10 == 0b10

Answer 2

You can add the Flag-attribute to the Enum

[Flags]
public enum Role
{
    NormalUser,
    Custodian,
    Finance,
    SuperUser = Custodian | Finance,
    All = Custodian | Finance | NormalUser
}

Then you can check for a role with this expression:

 Role testRole = Role.Finance
 if(testRole & Role.SuperUser == Role.SuperUser){
      //testRole is SuperUser
 }

Answer 3

Check out What does the [Flags] Enum Attribute mean in C#? for a more thorough explanation.

A "safer" way to declare flags is to use bit-shifting to ensure there's no overlap (as mentioned by @DaveOwen's answer) without figuring out the math yourself:

[Flags]
public enum MyEnum
{
    None   = 0,
    First  = 1 << 0,
    Second = 1 << 1,
    Third  = 1 << 2,
    Fourth = 1 << 3
}

There's also Enum.HasFlag (possibly newer .NET than OP) for checking, rather than Expected & Testing == Expected

Answer 4

Enum.HasFlag is what you want to use

Console.WriteLine("Custodian is in All: {0}", Role.All.HasFlag(Role.Custodian));

Just noticed that your enum should be defined like this with the Flags attribute and values spaced out by powers of 2

[Flags]
public enum Role
{
    NormalUser = 1,
    Custodian = 2,
    Finance = 4,
    SuperUser = Custodian | Finance,
    All = Custodian | Finance | NormalUser
}

The reason powers of 2 are used for flagged enums is that each power of 2 represents a unique bit being set in the binary representation:

NormalUser = 1 = 00000001
Custodian  = 2 = 00000010
Finance    = 4 = 00000100
Other      = 8 = 00001000

Because each item in the enum has a unique bit set this allows them to be combined by setting their respective bits.

SuperUser  = 6 = 00000110 = Custodian + Finance
All        = 7 = 00000111 = NormalUser + Custodian + Finance
NormOther  = 9 = 00001001 = NormalUser + Other

Notice how each 1 in the binary form lines up with the bit set for the flag in the section above.