Check/Compare a value using "in"

[MattCoder]

Hi,

I need to check if some value exists in a list (Array). To 
achieve that, I'm using Associative Arrays like this:

// Example
void main()
{
  int[char] aa = [ '+' :  0, '-' : 1];
  char ch = '+';

  if(ch in aa)
    // doSomething()...
}

But I'm looking for a more simple way like:

if(ch in ['+', '-'])    // <- This doesn't works
   // doSomething()...

Or another simple way (if exists of course).

Thanks.