spaceship-operator

问题 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? 回答1: 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

问题 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? 回答1: 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

问题 I was just reading the secret pseudo-constants, namely the Space fleet constant <=><=><=> Space fleet 0 This seems to be because the outer <=> is doing something I don't understand. My question is why does my $foo = <=>; Set $foo to = ? Other non-alphanumerics seem to work too, my $foo = <=>; my $foo = <->; my $foo = </>; But, alphanumerics don't... my $foo = <a>; Moreover, the perlsecret pod is confusing to me, Even though it looks like a sequence of three spaceship operators, only the

问题 I was just reading the secret pseudo-constants, namely the Space fleet constant <=><=><=> Space fleet 0 This seems to be because the outer <=> is doing something I don't understand. My question is why does my $foo = <=>; Set $foo to = ? Other non-alphanumerics seem to work too, my $foo = <=>; my $foo = <->; my $foo = </>; But, alphanumerics don't... my $foo = <a>; Moreover, the perlsecret pod is confusing to me, Even though it looks like a sequence of three spaceship operators, only the

问题 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

问题 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

问题 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. 回答1: 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): > , >= , ==

问题 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: a > b *equals* b < a == true a == b *equals* !(a < b) && !(b < a) Compared to using a trivalue* compare function, like for example Java, is this good for performance, or why was this design decision made? My assumption is that any trivalue compareto function still has to implement these

问题 This question already has answers here : Reference — What does this symbol mean in PHP? (18 answers) Closed 4 years ago . PHP 7, which will come out in November this year will introduce the Spaceship (<=>) operator. What is it and how does it work? This question already has an answer in our general reference question about PHP operators. 回答1: 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

问题 What is the Ruby <=> (spaceship) operator? Is the operator implemented by any other languages? 回答1: Perl was likely the first language to use it. Groovy is another language that supports it. Basically instead of returning 1 ( true ) or 0 ( false ) depending on whether the arguments are equal or unequal, the spaceship operator will return 1 , 0 , or −1 depending on the value of the left argument relative to the right argument. a <=> b := if a < b then return -1 if a = b then return 0 if a > b