[ruby-core:45472] [ruby-trunk - Feature #6555] New comparison operators

Issue #6555 has been updated by nobu (Nobuyoshi Nakada).

Description updated

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Feature #6555: New comparison operators
https://bugs.ruby-lang.org/issues/6555#change-27062

Author: jEFF (Jean-Fran巽ois Berroyer)
Status: Open
Priority: Normal
Assignee: 
Category: core
Target version: 2.0.0


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  x <=> y returns -1, 0, 1 or nil
  (x <=> y) == -1 means "x less than y" and is the same as x < y
  (x <=> y) == 0 means "x equal y" is the same as x == y
  (x <=> y) == 1 means "x greater than y" and is the same as x > y
  (x <=> y) == nil means "x not comparable with y" and is the same as !(x <=> y)
We see there is no short syntax to test if two objects are not comparable.
Can we have something like (({x >< y})), provided by (({Comparable})) module, that would mean "x and y are not comparable" ?

As (({x != y})) is a short syntax for (({!(x == y)})), can we have (({x !< y})) for (({!(x < y)})) and (({x !<= y})) for (({!(x <= y)})) and so on ?

As (({x <= y})) is the same as (({(x < y or x == y)})), can we have (({x <> y})) for (({(x < y or x > y)})) ?

Here is a list of all possible comparison operators there could be (and their meanings) :

  < return true when <=> return -1 ("less than")
  == return true when <=> return 0 ("egal")
  > return true when <=> return 1 ("greater than")
  <= return true when <=> return -1 or 0 ("equal or less than")
  >= return true when <=> return 1 or 0 ("equal or greater than")
  <> return true when <=> return 1 or -1 ("less or greater than" that is to say "comparable and different")
  >< return true when <=> return nil ("not comparable")
  !< return true when <=> return 0 or 1 or nil ("not less than", that is different from "greater than or eqal" that involves "comparable")
  != return true when <=> return -1 or 1 or nil ("not equal", that is different from "less or greater than" that involves "comparable")
  !> return true when <=> return -1 or 0 or nil ("not greater than", that is different from "less than or eqal" that involves "comparable")
  !<= return true when <=> return nil or 1 ("not equal nor less than", that is different from "greater than" that involves "comparable")
  !>= return true when <=> return nil or -1 ("not equal nor greater than", that is different from "less than" that involves "comparable")
  !<> return true when <=> return 0 or nil ("not less nor greater than", that is different from "egal" that involves "comparable")
  !>< return true when <=> return -1 or 0 or 1 ("not not comparable" or just "comparable", the same as <=> but returning a boolean)

All these operators would be very useful, especially when working with partial orders (like subset-inclusion for exemple).

Perhaps (({x !== y})) should also be a short syntax for (({!(x === y)})).
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