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c++c++20spaceship-operator
Ram
Ram

Reputation: 3133

Why do we need the spaceship <=> operator in C++?

Why do we need such an operator in C++ and how is it useful in modern C++ programming? Any real world code examples where this can be applied will help.

This question is geared to understanding the practical application in the real world.

Upvotes: 25

Views: 10286

Answers (1)

einpoklum
einpoklum

Reputation: 131523

I'll give you three points of motivation, just off the top of my head:

  1. It's the common generalization of all other comparison operator (for totally-ordered domains): >, >=, ==, <=, < . Using <=> (spaceship), you can implement each of these other operations in a completely generic way.
  2. For strings, it's equivalent to the good old strcmp() function from the C standard library. So - useful for lexicographic order checks, such as data in vectors or lists or other ordered containers.
  3. For integral numbers, it's what the hardware does anyway: On x86 or x86_64 Comparing a and b (CMP RAX, RBX) is basically like subtracting (SUB RAX, RBX) except that RAX doesn't actually change, only the flags are affected, so you can use "jump on equal/not equal/greater than/lesser than/etc." (JE/JNE/JGT/JLT etc.) as the next instruction. CMP should be thought of as a "spaceship compare".

Upvotes: 21

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