module Enumerable
def every_pair_with_indices
each_with_index do |a, i|
each_with_index do |b, j|
yield [a, b, i, j] if i < j
end
end
end
def every_pair
every_pair_with_indices do |a, b, i, j|
yield [a, b]
end
end
end

when breaking out of Enumerable#every_pair, JRuby 1.1.1 seems to break only out of the final implementation's inner loop, while MRI 1.8.6.p114 breaks out of the whole #every_pair (much like it would break out of #each):

ruby 1.8.6 (2008-03-03 patchlevel 114) [i686-linux]
>> [1,2,3,4].every_pair{|a,b| p [a,b]; break if [a,b] == [1,3]}
[1, 2]
[1, 3]
=> nil

ruby 1.8.6 (2008-04-22 rev 6555) [i386-jruby1.1.1]
>> [1,2,3,4].every_pair{|a,b| p [a,b]; break if [a,b] == [1,3]}
[1, 2]
[1, 3]
[2, 3]
[2, 4]
[3, 4]
=> [1, 2, 3, 4]