The 'in' operator does not works for arrays of basic types like int, string, etc.. it can be implemented as in lists with a comparator function:

Here's a sample code that fails to compile: (aka test case)

---
void main () {
        int[] foo = { 1, 3, 4, 10 };
        if (3 in foo) {
                print ("integer found\n");
        }
        string[] bar = { "foo", "bar", "cow" };
        if ("foo" in bar) {
                print ("string found\n");
        }
}
---