Use the Spaceship Operator <=> for Three-Way Comparisons
Learn to use the spaceship operator <=> for three-way comparisons.
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The three-way comparison operator (<=>), commonly called the spaceship operator because it looks like a flying saucer in profile, is new in C++20. You may wonder, what's wrong with the existing six comparison operators? Nothing at all, and we will continue using them. The purpose of the spaceship is to provide a unified comparison operator for objects.
The common two-way comparison operators return one of two states, true or false, according to the result of the comparison. For example:
const int a = 7;const int b = 42;static_assert(a < b);
The a < b expression uses the less-than comparison operator (<) to test if a is less than b. The comparison operator returns true if the condition is satisfied or false if not.
In this case, it returns true because