**diff options**

Diffstat (limited to 'lib/set.rb')

-rw-r--r-- | lib/set.rb | 19 |

1 files changed, 16 insertions, 3 deletions

@@ -45,9 +45,9 @@ # == Comparison # # The comparison operators <, >, <=, and >= are implemented as -# shorthand for the {proper_,}{subset?,superset?} methods. However, -# the <=> operator is intentionally left out because not every pair of -# sets is comparable ({x, y} vs. {x, z} for example). +# shorthand for the {proper_,}{subset?,superset?} methods. +# The <=> operator reflects this order, or return `nil` for +# sets that both have distinct elements ({x, y} vs. {x, z} for example). # # == Example # @@ -302,6 +302,19 @@ class Set end alias < proper_subset? + # Returns 0 if the set are equal, + # -1 / +1 if the set is a proper subset / superset of the given set, + # or nil if they both have unique elements. + def <=>(set) + return unless set.is_a?(Set) + + case size <=> set.size + when -1 then -1 if proper_subset?(set) + when +1 then +1 if proper_superset?(set) + else 0 if self.==(set) + end + end + # Returns true if the set and the given set have at least one # element in common. # |