Check if a variable is in an ad-hoc list of values

Question

Is there a shorter way of writing something like this:

if(x==1 || x==2 || x==3) // do something

What I'm looking for is something like this:

if(x.in((1,2,3)) // do something

Answer 1

You could achieve this by using the List.Contains method:

if(new []{1, 2, 3}.Contains(x))
{
    //x is either 1 or 2 or 3
}

Answer 2

public static bool In<T>(this T x, params T[] set)
{
    return set.Contains(x);
}

...

if (x.In(1, 2, 3)) 
{ ... }

Required reading: MSDN Extension methods

Answer 3

If it's in an IEnumerable<T>, use this:

if (enumerable.Any(n => n == value)) //whatever

Else, here's a short extension method:

public static bool In<T>(this T value, params T[] input)
{
    return input.Any(n => object.Equals(n, value));
} 

Put it in a static class, and you can use it like this:

if (x.In(1,2,3)) //whatever