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c#enumsbit-manipulationflags
Gil Stal
Gil Stal

Reputation: 3458

Enums - All options value

Is there a way to add an "All values" option to an enum without having to change its value every time a new value is added to the enum?

[Flags] 
public enum SomeEnum
{
    SomeValue =  1,
    SomeValue2 = 1 << 1,
    SomeValue3 = 1 << 2,
    SomeValue4 = 1 << 3,
    All = ?
}

Update:

Ended up inheriting from long and using long.MaxValue for All option.

Upvotes: 27

Views: 16247

Answers (8)

Anders Forsgren
Anders Forsgren

Reputation: 11101

Since you should define the empty value in a Flags enum such as None = 0, the simplest way of defining the Allvalue is by simply inverting all the bits inNone`.

[Flags]
enum MyEnum
{
   None = 0,
   A = 1,
   B = 2,
   C = 4,
   ...
   All = ~None
}

Note that ~0 instead of ~None will not work for unsigned backing types as that is -1, which is not a valid value for unsigned.

Edit: Answer was modified to use an inverted None instead of an explicit constant such as 0x7FFFFFFF or ~0, as this also works for unsigned

Upvotes: 44

j0hn570n3
j0hn570n3

Reputation: 1

public static T EnumSetAll<T>() where T : struct, Enum
  {
    string str = string.Join(", ", Enum.GetNames(typeof(T)));

    if (Enum.TryParse<T>(str, out var e))
      return e;

    return default;
  }

Upvotes: 0

Dai
Dai

Reputation: 155055

This is possible if you're okay with a static readonly field in a separate type, rather than as a const enum field:

[Flags] 
public enum SomeEnum
{
    None       = 0,
    SomeValue  = 1,
    SomeValue2 = 1 << 1,
    SomeValue3 = 1 << 2,
    SomeValue4 = 1 << 3,
}

public static class SomeEnumUtility {

    private static readonly SomeEnum[] _someEnumValues = (SomeEnum[])Enum.GetValues( typeof(SomeEnum) );
    public static readonly SomeEnum SomeEnum_All = GetSomeEnumAll();

    // Unfortunately C# does not support "enum generics" otherwise this could be a generic method for any Enum type
    private static SomeEnum GetSomeEnumAll() {

        SomeEnum value = SomeEnum.None; // or `(SomeEnum)0;` if None is undefined.
        foreach(SomeEnum option in _someEnumValues) {
            value |= option;
        }
        return value;
    }
}

Then you can get SomeEnumUtility.SomeEnum_All. As it's a static readonly the computation is only performed once, in a thread-safe manner.

As I wrote in the code-comment, it's unfortunate that C# does not support enum generics, otherwise you could do this:

    private static TEnum GetEnumAllFlags<TEnum>() where TEnum : enum {

        TEnum[] allValues = Enum.GetValues<TEnum>();

        TEnum value = (TEnum)0;
        foreach(TEnum option in allValues) {
            value |= option;
        }
        return value;
    }

Oh well :(

Upvotes: 0

Dmitriy Konovalov
Dmitriy Konovalov

Reputation: 1817

It should be like this:

[Flags] 
public enum SomeEnum
{
    SomeValue =  1,
    SomeValue2 = 1 << 1,
    SomeValue3 = 1 << 2,
    SomeValue4 = 1 << 3,
    All = SomeValue | SomeValue2 | SomeValue3 | SomeValue4
}

Upvotes: 18

Askolein
Askolein

Reputation: 3378

An enum can be made of many different length integer types (short, int, long). This makes the #FFFFFFFF solution inappropriate (as pointed out in @MarcGravell comment).

An enum can be made of unsigned types (uint for isntance). This makes the -1 solution inappropriate.

My best bet is, maintenance-free:

All = ~0

Upvotes: 5

m1o2
m1o2

Reputation: 1629

You can use a little trick

(SomeEnum)( (1 << ( Enum.GetValues( typeof(SomeEnum) ).Length ) ) -1 )

If you added a 'None' Enum name with value = 0 ( None = 0, ) then you need to put a '-1' after the Length.

Upvotes: 0

Ofir
Ofir

Reputation: 2194

The Idea is to use the behavior of the enum to calculate the last value.

Add Last field after all 'real' enum values.

Add All field equals to (Last << 1) - 3.

[Flags]
public enum SomeEnum
{
    SomeValue =  1,
    SomeValue2 = 1 << 1,
    SomeValue3 = 1 << 2,
    SomeValue4 = 1 << 3,

    // Do not add values after this
    Last,
    All = (Last << 1) - 3,
}

I answered it at: How to use Enum with aditional options (All, None)

You can check my blog at Enum Trick for more information and ideas.

Upvotes: 3

Oded
Oded

Reputation: 498932

No, there is nothing built is that will make such an All option automatically update when the Enum changes.

You may want to have a special value (monitor value) that means All (say -1), even if it is not the bitwise sum of all of the options.

An alternative is to use a value that has all of the bits switched on:

All = 0xFFFFFFFF

Upvotes: 2

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