C#. Do if( a == (b or c or d)). Is it possible?

Question

Is there another way to write something like this:

if (a == x || a == y || a == z)

One way that I found is doing it like this:

Answer 1

Your solution to rewrite it as

if( new [] {x,y,z}.Contains(a))

is not a good move.

You've take a simple efficient logical operation, which every programmer easily understands and which contains short-circuiting logic to speed it up and instead you've produced code that requires a moment to understand and which is considerably less efficient.

Sometimes your fellow engineers will prefer it if you don't try to be "clever"!

Answer 2

if(a==x?true:a==y?true:a==z?true:false)

Answer 3

For instance, your logic is like that:

if(a==x || a== y|| a==z)
{
    DoSomething();
} 
else
{
   DoOtherThings();
}

will equivalent to:

if(a!=x&& a != y && a!= z)
{
   DoOtherThings();
}
else
{
   DoSomething();
}

Cheers.

Answer 4

Consider a case where a == x, and y and z are slow-to-evaluate, expensive functions.

• In if(a == x || a == y || a == z) you have the benefit of the short-circuit ||-operator, so you y and z won't be evaluated.
• If you make an array with new[] { x, y, z } - y and z will be evaluated every time.

The 'trick' with .Contains() would be more useful if there was an elegant syntax to create lazy-evaluated sequence (IEnumerable<T>). i.e. something like yield return x; yield return y;..., but inlined and shorter.

Answer 5

Why would you need yet another way? Since it isn't a matter of functionality, I would guess the point is to improve readability. If you have a few variables with meaningful names, it would be more readable to just compare by using ==. If you have more, you can use Contains against a list as in your other sample. Yet another way would be comparing against enum flags:

[Flags]
public enum Size
{
    Small = 1,
    Medium = 2,
    Large = 4
}

And then to find out if mySize is in Small or Medium:

selectedSizes = Size.Small | Size.Medium;
mySize = Size.Small;
if (mySize & selectedSizes)
{
  ... 
}