Hello
I found this to be somewhat amusing:
a = []
=> []a.all?
=> truea.all? { |i| i == 10 }
=> true
Is there any reasoning for Enumerable#all? to always return true for
empty arrays?
Best regards,
Andre
On Thu, 10 Aug 2006, Andre N. wrote:
Is there any reasoning for Enumerable#all? to always return true for
empty arrays?Best regards,
Andre
well - it’s either that or false. we’d need maybe for it to really make
sense.
consider
[].all?{|x| x.nil?} # true or false??
either is arbitrary
-a
Andre N. wrote:
=> true
a.all? { |i| i == 10 }
=> true
Is there any reasoning for Enumerable#all? to always return true for
empty arrays?
It’s what modern logic says… or something like it.
Andre N. wrote:
=> true
Is there any reasoning for Enumerable#all? to always return true for
empty arrays?
I think they are modeled after universal and existential quantifiers in
predicate calculus:
a.all?(&b) is true iff for all x in a b[x].
This leads to a.all? being true.
a.any?(&b) is true iff there exists an x in a for which b[x].
This leads to a.any? being false.
On Thu, Aug 10, 2006 at 01:41:48AM +0900, Andre N. wrote:
Is there any reasoning for Enumerable#all? to always return true for
empty arrays?
a.all?{ … } == true
can be read as “All elements in a satisfy { … }”, which we can
interpret as
“there is no element in a such that { … } is not satisfied”, which is
obviously true if a is empty.
On Thu, 2006-08-10 at 03:03 +0900, Mauricio F. wrote:
can be read as “All elements in a satisfy { … }”, which we can interpret as
“there is no element in a such that { … } is not satisfied”, which is
obviously true if a is empty.
OK, thank you all for the explanations 
Andre
On Thu, Aug 10, 2006 at 08:55:12AM +0900, Just Another Victim of the
Ambient M. wrote:
=> true
say the condition is true…
unless mathematician.is_an :intuitionist # (pretty rare)
Sorry I couldn’t resist
-Jürgen
“Andre N.” [email protected] wrote in message
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Is there any reasoning for Enumerable#all? to always return true for
empty arrays?
It's mathematically consistent.
You may be surprised to hear this but mathematicians are generally
optimists. Thus, if a condition is “vacuously satisfied,” then we
generally
say the condition is true…