Not infrequently, one wants to implement the <=> (comparison, or "spaceship") operator on a product data type, i.e., a class with multiple fields (all of which (we hope!) already have <=&g...

What are their differences? Coming from a Java background, it does seem to me <=> is the same as Java's equals(), while == is for direct reference comparison. Is this right?

Why was the spaceship operator <=> chosen to have one equal sign rather than two? Is this seen as inconsistent with one equal sign usually meaning assignment, and two meaning comparison?

I am confused with Ruby's <=> operator. How does it differ from == or ===? Any comprehensive examples/use case? Thanks.

In C++/STL sorting is done by using only the less-than operator. Altough I have no idea how the sorting algorithms are actually implemented, I assume that the other operations are created implicite...

I've only seen the Perl spaceship operator (<=>) used in numeric sort routines. But it seems useful in other situations. I just can't think of a practical use. What would be an example of whe...