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Questions tagged [spaceship-operator]

The <=> comparison operator is often referred to as the spaceship operator. It performs a 3-way comparison (returning less, equal, or greater) on the two operands.

The spaceship operator (so named because of its appearance) is used to compare items for sorting in various languages (such as Perl, Ruby, and Groovy). The standard definition is that:

  • a <=> b is less than zero if a < b
  • a <=> b is zero if a == b
  • a <=> b is greater than zero if a > b

The spaceship operator can also be used to provide default implementations of the <, >, and even == operators if the language (or libraries) is clever enough.

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What is the Ruby <=> (spaceship) operator?

What is the Ruby <=> (spaceship) operator? Is the operator implemented by any other languages?
Justin Ethier
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What is the <=> ("spaceship", three-way comparison) operator in C++?

While I was trying to learn about C++ operators, I stumbled upon the following table that listed a strange comparison operator. What does this <=> operator do? Since 2017 cppreference.com updated that page and now contains detailed information…
q-l-p
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What is <=> (the 'Spaceship' Operator) in PHP 7?

PHP 7 introduced the Spaceship (<=>) operator. What is it and how does it work?
Deepak Mankotia
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What is this operator <=> in MySQL?

I'm working on code written by a previous developer and in a query it says, WHERE p.name <=> NULL What does <=> mean in this query? Is it something equal to =? Or is it a syntax error? But it is not showing any errors or exceptions. I already know…
zzlalani
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C++20 behaviour breaking existing code with equality operator?

I ran into this while debugging this question. I trimmed it down all the way to just using Boost Operators: Compiler Explorer C++17 C++20 #include struct F : boost::totally_ordered1> { …
sehe
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non-defaulted operator <=> doesn't generate == and != in C++20

I'm running into a strange behavior with the new spaceship operator <=> in C++20. I'm using Visual Studio 2019 compiler with /std:c++latest. This code compiles fine, as expected: #include struct X { int Dummy = 0; auto…
Zeenobit
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How is the three-way comparison operator different from subtraction?

There's a new comparison operator <=> in C++20. However I think in most cases a simple subtraction works well: int my_strcmp(const char *a, const char *b) { while (*a == *b && *a != 0 && *b != 0) { a++, b++; } // Version 1 …
iBug
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Why must I provide 'operator ==' when 'operator <=>' is enough?

#include struct A { int n; auto operator<=>(A const& other) const { if (n < other.n) { return std::strong_ordering::less; } else if (n > other.n) { return…
xmllmx
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More silent behaviour changes with C++20 three-way comparison

To my surprise, I ran into another snag like C++20 behaviour breaking existing code with equality operator?. Consider a simple case-insensitive key type, to be used with, e.g., std::set or std::map: // Represents case insensitive keys struct CiKey :…
sehe
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Combined Comparison / "Spaceship" Operator (<=>) in Javascript?

Ruby has something called a Combined Comparison or "Spaceship" Operator, it looks like this: <=> It does the following: a <=> b := if a < b then return -1 if a = b then return 0 if a > b then return 1 Credit Is there a similar…
Kaspar Lee
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Is the three-way comparison operator always efficient?

Herb Sutter, in his proposal for the "spaceship" operator (section 2.2.2, bottom of page 12), says: Basing everything on <=> and its return type: This model has major advantages, some unique to this proposal compared to previous proposals for C++…
Cris Luengo
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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 understand the practical application in real world without reading…
Ram
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Practical meaning of std::strong_ordering and std::weak_ordering

I've been reading a bit about C++20's consistent comparison (i.e. operator<=>) but couldn't understand what's the practical difference between std::strong_ordering and std::weak_ordering (same goes for the _equality version for this manner). Other…
Mr. Anderson
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Three-way comparison and constexpr function template: which compiler is right?

Consider: #include template constexpr int f() { return 1; } unsigned int x; using T = decltype(x <=> f()); GCC and MSVC accept the declaration of T. Clang rejects it, with the following error message: :7:26: error:…
cpplearner
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Is there a std::less/std::greater for the spaceship operator?

All the basic comparisons (<, <=, ==, !=, >=, >) have an associated function object (std::less, std::less_equal, std::equal_to, std::not_equal_to, std::greater_equal, std::greater). Does the spaceship operator <=> have a similar function object? If…
rubenvb
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