Question

Is it possible with a ONE-Liner (else the normal way…) to check if any of all possible enum states are set?

From enum fruits I want to know wether it is unset means no banana, no apple, no melon.

How can I do that?

Answer 1

Would:

myFlags == 0

Suffice? 0 represents no bits set, assuming you are using flags and not doing anything funky with the values.

Given this enum:

[Flags]
enum Fruit
{
    Forbidden = 0,
    Apple = 1,
    Orange = 2,
    Banana = 4
}

And this code:

Fruit f = Fruit.Apple | Fruit.Banana;

if (f == 0)
    MessageBox.Show("what?");

f = Fruit.Forbidden;

if (f == 0)
    MessageBox.Show("expected");

It does what you’d expect it to, however it is checking the underling value not doing bitwise ops, so if you mutate the underling value incorrectly you start to get issues, but you’ll get other issues as well.

Given:

[Flags]
enum Fruit
{
    Apple = 1,
    Orange = 2,
    Banana = 4
}

And:

Fruit f = Fruit.Apple | Fruit.Banana;

if (f == 0)
    MessageBox.Show("what?");

f = f & ~Fruit.Apple & ~Fruit.Banana;

if (f == 0)
    MessageBox.Show("expected");

Also behaves.