isLessThan function for structure with 7 integers

Question

The objective

I was trying to create a function that would compare 7 different integers. It should be able to be used to:

• Sort the two structures in a consistent manner
• Be able to detect if two structures are equal with !isLessThan(a,b) && !isLessThan(b,a)

The code

At first, I thought of using a hash function to reduce all the values to one, but then it occurred to me that I was over-engineering this simple problem.

This is language agnostic, but I ended up doing it like this:

bool isLessThan(const MyStruct& lhs, const MyStruct& rhs) {
    return
        lhs.a +
        lhs.b * 2 +
        lhs.c * 3 +
        lhs.d * 4 +
        lhs.e * 5 +
        lhs.f * 6 +
        lhs.g * 7
            <
        rhs.a +
        rhs.b * 2 +
        rhs.c * 3 +
        rhs.d * 4 +
        rhs.e * 5 +
        rhs.f * 6 +
        rhs.g * 7;
}

Answer 1

Don't re-invent the wheel (unless of course you want practice at doing that):

1. Instead of naming a bunch of elements that are all the same type, use an array for your structure's elements like std::array, or use a std::tuple. Or if you really don't want to change your structure's content, use std::tie to craft a tuple of your structure's elements on demand.
2. If you used a regular array use std::lexicographical_compare on the iterable elements of the two structures. A std::array or std::tuple already has non-member function support for operators like <, <=, >=, etc. though.
3. Kick back and enjoy a brewski. ;) (only if allowed of course and be sure to drink responsibly etc. etc.).

Answer 2

Some things that caught my eye:

You haven't mentioned the specific criteria that would make one struct less than another.

If the variables' values aren't sorted, it is entirely likely to get false positives with your approach.

If g is greater than INT_MAX / 7, or f is greater than INT_MAX /6, etc., or if the total is greater than INT_MAX, your code will throw a fatal error.

Answer 3

there is an easy way to do this:

auot const& left  = std::make_tuple(lhs.a, lhs.b, lhs.c, lhs.d, lhs.e, lhs.f, lhs.g);
auto const& right = std::make_tuple(rhs.a, rhs.b, rhs.c, rhs.d, rhs.e, rhs.f, rhs.g);

return left < right;