How to set all bits of an enum flag in C#

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snippet csharp

In C#, you can use the [Flags] attribute to create an enum type as bit flags, allowing you to use Bitwise operations.

Let's take an example of Seasons


[Flags]
public enum Seasons
{
    None = 0,
    Spring = 1 << 0,
    Winter = 1 << 1,
    Autumn = 1 << 2,
    Summer = 1 << 3
}

Sometimes, we want to set all the bits on a flag. The easiest way to do this is by adding another value to the enum by manually combining all the bits yourself.

[Flags]
public enum Seasons
{
    ... // omitted for brevity
    All = Spring | Winter | Autumn | Summer
}

But, this has a small problem. Every time we add a new value to the enum, we must update the All value.

Here is a simple trick to get a variable with all the bits set.

 var AllSeasons = (Seasons)Enum.GetValues<Seasons>().Cast<int>().Sum();

Let's see what's happening in the above snippet.

Enum.GetValues() returns an array of the enums values.

Cast cast the elements of the array to its int values. Remember that the underlying type of an enum is int.

Sum computes the sum of all the values in the collection.

We then cast it back to Seasons.

Conclusion

Using Linq magic, we can get an enum value with all the flags set without adding an All value to the enum.

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