[].all?{} and [].any?{} Behavior
in [Ruby]
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From: John Sikora on 29 Jul 2010 17:27 I find the following behavior interesting (so interesting that I modified it), and I would like to hear others' thoughts on the subject: [3].all? {|element| element == 3 } # => true [3].all? {|element| element != 3 } # => false (sanity checks) [].all? {|element| element == 3 } # => true [].all? {|element| element != 3 } # => true [].any? {|element| element == 3 } # => false [].any? {|element| element != 3 } # => false Ruby 1.8.6 and 1.9.1 both give these results. The first interesting thing is that both the == and the != checks give the same logical result (always true for all?, always false for any?). After thinking about it a little, I decided that this is the desired behavior. I also understand why it happens. For example, in the case of all?, the documentation says that true will be the result if the block never returns false or nil. In the case of [], the block never gets called, so the result is true. I know the block never gets called because the following does not print anything: [].all? {|dummy| puts 'print something'}, while [3].all? {|dummy| puts 'print something'} does. The second interesting thing is that a result of this behavior is that for the same check, all? will give a result of true, while any? will give a result of false. This seems contradictory. I would prefer that for [], both all? and any? would give a result of false for any check. So I have over-ridden Array#all?, returning false if self == []. My main motivation for doing so is in situautions such as: obj_array.find_all{|obj| obj.attr_1 == x}.all?{|obj| obj.attr_2 == y} If the find_all returns [], I want the all? result to be false, not true. I assume that others have run across this but some quick searches did not turn up anything. I am wondering how others deal with this such as over-riding as I do, checking for [] each time (which does not seem very Ruby-like), or even leaving the operation as is because for some, it may be the desired behavior. Finally, are there any potential detrimental effects that might occur due to the behavior modification that I made. I am not a Rails user (if that matters), I mainly use Ruby for scripting and hardware control applications (and I am interested in learning as much as I can about Ruby because I like it so much). js -- Posted via http://www.ruby-forum.com/.
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