The spaceship operator is an attempt to achieve the same thing as Rust's PartialOrd -- to have a single authoritative place to explain the ordering of a type.

The spaceship operator is an attempt to achieve the same thing as Rust's PartialOrd -- to have a single authoritative place to explain the ordering of a type. Historically C++ only had these separate comparison operators, and operator overloading, and so if you want ordering you'd be expected to override all of the operators and do so in a consistent way. Turns out it's easy enough to get that wrong and if you do now your C++ program is often nonsense, it has no defined meaning whatsoever. For example if a < b && b < a then too bad now many built-in library functions might do absolutely anything in say C++ 17. With the spaceship operator you're still screwed if your type provides an incoherent ordering (unlike Rust where that just means the type is less useful) but it's much more likely you'll write something which actually works.