import std.stdio;
void main()
{
    string[int] numbers = [ 0 : "zero", 1 : "one", 2 : "two", 3 : "three" ];
int number = 2;
auto element = number in numbers;
if (element) {
    writefln("I know: %s.", *element);
} else {
    writefln("I don't know the spelling of %s.", number);
    }
}