Since C++20, a three-way comparison operator (a "spaceship" operator <=>) is available [1].

The codebase uses C++20 since commit 1eef07805021b7ca26a1a8894809b6d995747ba1.

In cases where we have a full set of comparison operators, it could be beneficial to replace them all with such a three-way operator, to benefit from code deduplication. Indeed, this needs to take performance into account.

In many cases, the implementation of the operator may also be simplified from something like

>    if (a < other.a)
>        ...
>    else if (a == other.a && b < other.b)
>        ...

into more idiomatic

>   return std::tie(a, b) <=> std::tie(other.a, other.b);

Sometimes there is no full set of comparison operators in a class, and only e.g. operator < is defined. In such cases, the three-way comparison would be unnecessary; but the simplification of the implementation comparing std::tie could still be used.

When simplifying the implementations in such a way, performance needs to also be taken into account: e.g., some calculations should only be performed after previous comparisons were done, which would not happen, if everything would be passed to std::tie at once.

This is an easyhack that can be worked on in parallel. Please don't do a large-scale change over the whole codebase; only change one or two files at a time. Do not assign this issue to you, because of the parallel nature of the task.

[1] https://en.cppreference.com/w/cpp/language/operator_comparison#Three-way_comparison