From: John Sikora <john.sikora@...>
Date: 2010-07-31T03:22:44+09:00
Subject: Re: .any?{} Behavior

Rick Denatale wrote:

> By convention the universal quantifier evaluates to true for an empty 
> set:
> http://en.wikipedia.org/wiki/Universal_quantification#The_empty_set
> http://en.wikipedia.org/wiki/Vacuous_truth
>>

Well, that seals it for me. My thinking is wrong if it goes against 
convention, not only in Ruby, but in universal quantification.

> 
> For library code, such as in a gem I think it would be better to think
> up some other method name rather than changing the standard, e.g.
> 
> module Enumerable
>   def non_vacuous_all?(&b)
>     !empty? && all?(&b)
>   end
> end
> 
> [3].all? {|element| element == 3 }  # => true
> [3].all? {|element| element != 3 }  # => false
> 
> [].all? {|element| element == 3 }   # => true
> [].all? {|element| element != 3 }   # => true
> 
> [3].non_vacuous_all? {|element| element == 3 }  # => true
> [3].non_vacuous_all? {|element| element != 3 }  # => false
> 
> [].non_vacuous_all? {|element| element == 3 }   # => false
> [].non_vacuous_all? {|element| element != 3 }   # => false
> 
> [].any? {|element| element == 3 }   # => false
> [].any? {|element| element != 3 }   # => false
> 
> There may be a better name than non_vacuous_all? but I can't think of 
> one.
> 

Agreed, I should use a similar technigue for my specific applications.

js
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