D Language Associative Arrays Check if a key exist
Example
int[string] numbers = ["a" : 10, "b" : 20];
assert("a" in numbers);
assert("b" in numbers);
assert("c" in numbers);
int[string] numbers = ["a" : 10, "b" : 20];
assert("a" in numbers);
assert("b" in numbers);
assert("c" in numbers);
