The principle reason why equality and ordering are separated is performance. If you have a type whose ordering operations are user-defined, then more often than not, you can write a user-defined equality test operation that is more efficient at doing equality tests. And therefore, the language should encourage you to write it by not using … Read more
This is by design. [class.compare.default] (emphasis mine) 3 If the class definition does not explicitly declare an == operator function, but declares a defaulted three-way comparison operator function, an == operator function is declared implicitly with the same access as the three-way comparison operator function. The implicitly-declared == operator for a class X is an … Read more
This is called the three-way comparison operator. According to the P0515 paper proposal: There’s a new three-way comparison operator, <=>. The expression a <=> b returns an object that compares <0 if a < b, compares >0 if a > b, and compares ==0 if a and b are equal/equivalent. To write all comparisons for … Read more
TL;DR It’s the NULL safe equal operator. Like the regular = operator, two values are compared and the result is either 0 (not equal) or 1 (equal); in other words: ‘a’ <=> ‘b’ yields 0 and ‘a’ <=> ‘a’ yields 1. Unlike the regular = operator, values of NULL don’t have a special meaning and … Read more
The <=> (“Spaceship”) operator will offer combined comparison in that it will : Return 0 if values on either side are equal Return 1 if the value on the left is greater Return -1 if the value on the right is greater The rules used by the combined comparison operator are the same as the … Read more
It’s also known as the Three-Way Comparison Operator. Perl was likely the first language to use it. Some other languages that support it are Apache Groovy, PHP 7+, and C++20. The spaceship operator will return 1, 0, or −1 depending on the value of the left argument relative to the right argument. a <=> b … Read more