d test

/*
bool foo(T)(const(char)[] id, T arg)
if (is(T : const(char)[]) || is(T : const(char[])[]))
{
        static if (is(T : const(char)[])) {
                return id == arg;
        } else {
                foreach (s; arg) if (s == id) return true;
        }
        return false;
}
*/

bool foo(const(char)[] id, const(char[])[]  arg ...)
{
    foreach (s; arg) if (s == id) return true;
    return false;
}

void main()
{
    string id = "id";

    char[] a = "aaaa".dup;
    const(char)[] b = "bbbb";
    immutable(char)[] c = "cccc";
    foo(id, a);
    foo(id, b);
    foo(id, c);
    char[][] aa = ["aaaa".dup];
    const(char)[][] bb = ["bbbb"];
    immutable(char)[][] cc = ["cccc"];
    foo(id, aa);
    foo(id, bb);
    foo(id, cc);

    // these works with the typesafe variadic function only
    foo("id", "aaaa", "bbbb");
    foo("id", "aaaa", "bbbbb", "cccc");

    // these should always fail
    dstring w = "wwww";
    dstring[] ww = ["wwww"];
    foo(id, w);
    foo(id, ww);
}