Enumerable#all? and empty arrays

[Andre Nathan]

Hello

I found this to be somewhat amusing:

a = [] => []
a.all? => true
a.all? { |i| i == 10 }

=> true

Is there any reasoning for Enumerable#all? to always return true for
empty arrays?

Best regards,
Andre

 

[ara.t.howard]

Hello

I found this to be somewhat amusing:

a = [] => []
a.all? => true
a.all? { |i| i == 10 }

=> true

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

 

[Carlos]

Hello

I found this to be somewhat amusing:

a = []

=> []

=> true

=> 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.

http://en.wikipedia.org/wiki/Square_of_opposition#The_problems_of_existential_import

--

 

[Florian Frank]

a = []

=> []
=> true
=> 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.

 

[Mauricio Fernandez]

Hello

I found this to be somewhat amusing:

a = [] => []
a.all? => true
a.all? { |i| i == 10 }

=> true

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.

 

[Andre Nathan]

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

 

[Just Another Victim of the Ambient Morality]

Hello

I found this to be somewhat amusing:

a = [] => []
a.all? => true
a.all? { |i| i == 10 }

=> true

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...