What is the Ruby spaceship operator

Question

What is the Ruby  lt   gt   spaceship  operator  Is the operator implemented by any other languages

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I will explain with simple example   1 3 2   lt   gt   2 2 2  Ruby will start comparing each element of both array from left hand side  1 for left array is smaller than 2 of right array  Hence left array is smaller than right array  Output will be -1    2 3 2   lt   gt   2 2 2  As above it will first compare first element which are equal then it will compare second element  in this case second element of left array is greater hence output is 1

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It s a general comparison operator  It returns either a -1  0  or  1 depending on whether its receiver is less than  equal to  or greater than its argument

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Since this operator reduces comparisons to an integer expression  it provides the most general purpose way to sort ascending or descending based on multiple columns attributes    For example  if I have an array of objects I can do things like this      sort   modifies array in place  avoids duplicating if it s large       Sort by zip code  ascending my objects sort     a  b  a zip  lt   gt  b zip      Sort by zip code  descending my objects sort     a  b  b zip  lt   gt  a zip        same as    my objects sort     a  b  -1    a zip  lt   gt  b zip       Sort by last name  then first my objects sort     a  b  2    a last  lt   gt  b last     a first  lt   gt  b first       Sort by zip  then age descending  then last name  then first    Notice powers of 2 make it work for  gt  2 columns   my objects sort  do  a  b        8    a zip    lt   gt  b zip         -4    a age    lt   gt  b age          2    a last   lt   gt  b last               a first  lt   gt  b first  end   This basic pattern can be generalized to sort by any number of columns  in any permutation of ascending descending on each

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What is  lt   gt     The  Spaceship  Operator     According to the RFC that introduced the operator   a  lt   gt   b   -  0 if  a     b  - -1 if  a  lt   b  -  1 if  a  gt   b      - Return 0 if values on either side are equal  - Return 1 if value on the left is greater  - Return -1 if the value on the right is greater   Example     Comparing Integers  echo 1  lt   gt  1    ouputs 0 echo 3  lt   gt  4    outputs -1 echo 4  lt   gt  3    outputs 1    String Comparison  echo  x   lt   gt   x      0 echo  x   lt   gt   y     -1 echo  y   lt   gt   x     1   MORE      Integers echo 1  lt   gt  1     0 echo 1  lt   gt  2     -1 echo 2  lt   gt  1     1     Floats echo 1 5  lt   gt  1 5     0 echo 1 5  lt   gt  2 5     -1 echo 2 5  lt   gt  1 5     1     Strings echo  a   lt   gt   a      0 echo  a   lt   gt   b      -1 echo  b   lt   gt   a      1  echo  a   lt   gt   aa      -1 echo  zz   lt   gt   aa      1     Arrays echo     lt   gt         0 echo  1  2  3   lt   gt   1  2  3      0 echo  1  2  3   lt   gt         1 echo  1  2  3   lt   gt   1  2  1      1 echo  1  2  3   lt   gt   1  2  4      -1     Objects  a    object    a    gt   b      b    object    a    gt   b     echo  a  lt   gt   b     0

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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  lt   gt  b      if a  lt  b then return -1   if a   b then return  0   if a  gt  b then return  1   if a and b are not comparable then return nil   It s useful for sorting an array

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The spaceship method is useful when you define it in your own class and include the Comparable module  Your class then gets the  gt    lt     gt     lt        and between  methods for free   class Card   include Comparable   attr reader  value    def initialize value       value   value   end    def  lt   gt   other   1 if self gt other  0 if self  other  -1 if self lt other     self value  lt   gt  other value   end  end  a   Card new 7  b   Card new 10  c   Card new 8   puts a  gt  b   false puts c between  a b    true    Array sort uses  lt   gt    p  a b c  sort      lt Card 0x0000000242d298  value 7 gt     lt Card 0x0000000242d248  value 8 gt     lt Card 0x0000000242d270  value 10 gt

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