bool less(T)(T left, T right) {
    return left < right;
}

template lessBy(alias get) {
    static bool lessBy(T)(T left, T right) {
        return less(get(left), get(right));
    }
}

bool more(T)(T left, T right) {
    return left > right;
}

template moreBy(alias get) {
    static bool moreBy(T)(T left, T right) {
        return more(get(left), get(right));
    }
}

void main(string[] argv) {
    import std.algorithm;

    struct Person {
        int firstName;
        int lastName;
    }

    Person[] testArr;

    testArr.sort!(lessBy!(x => x.firstName))();
    testArr.sort!(moreBy!(x => x.lastName))();