The zero value for a map is nil. The zero value for a struct is a valid struct whose fields are all zeroed. So for pair, that would be (0, 0). The zero value

The zero value for a map is nil. The zero value for a struct is a valid struct whose fields are all zeroed. So for pair, that would be (0, 0). The zero value for a pointer is nil. If you had said `var p *pair`, then it would be a pointer to pair, and it would be nil, and you would get a nil panic error.