spaceship-operator

In " Is it possible to sort a list of objects depending on if the individual object's response to a method? ", I discovered that the flying saucer doesn't work on booleans. Consider: Ruby 1.8.7: [true, false].sort # => undefined method `<=>' for true:TrueClass (NoMethodError) true <=> false # => undefined method `<=>' for true:TrueClass (NoMethodError) Ruby 1.9.3: [true, false].sort # => comparison of TrueClass with false failed (ArgumentError) true <=> false # => nil true <=> true # => 0 false <=> true # => nil It may have something to do with true and false not having a canonical sort order,

This is a best practice question. 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. Can anyone give me an example of when it could be used outside of a Perl sort? I'm writing a control system for robot Joe that wants to go to robot Mary and recharge her. They move along the integer points on the line. Joe starts at $j and can walk 1 meter in any direction per time unit. Mary stands still at $m and can't move -- she needs a good recharge! The controlling program would look like that:

Context While I was reading Consistent comparison , I have noticed a peculiar usage of the verb to compare : 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. Another example found on the internet (emphasis mine): It returns a value that compares less than zero on failure. Otherwise, the returned value can be used as the first argument on a later call to get. One last example , found in a on GitHub (emphasis mine): // Perform a circular 16 bit compare.

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 Operator in Javascript? If not, how can I end up with the same result? @madox2 suggested using Math.sign(a - b) , which works for number, but not arrays (to compare arrays you need to use array.length ). It also does not work in Internet Explorer, Safari or all Mobile Browsers (see MDN ) @duques_l found a function here . It works very well, you can test it on JSFiddle

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 wordy proposal from Herb Sutter. No offense to the proposal though. I'll give you three points of motivation, just off the top of my head: 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

In a recently published paper [1], Herb Sutter et al. describe an extension of the programming language C++ by a three way comparison operator. The authors refer to a considerable number of earlier proposals, all of which were ultimately rejected. The clever core concept of the new approach is to encode different categories of relations in the return type of the comparison operator. The authors declare that The primary design goal is conceptual integrity [Brooks 1975], which means that the design is coherent and reliably does what the user expects it to do. A total of five categories of