From: 7stud -- <bbxx789_05ss@...>
Date: 2008-05-09T16:18:47+09:00
Subject: Re: Doing an AND in regexp char class

Joel VanderWerf wrote:
> Todd Benson wrote:
>>>>
>>>> Thanks,
>>> p 'foobar'.all_chars?('')
>>>
>>>
>>>
>>> cfp:~ > ruby a.rb
>>> true
>>> false
>>> false
>> 
>> Cool :)  #tr is one of those useful methods I somehow consistently forget about.
> 
> But it can be done with regex, right? It's just more elegant with tr.
> 
> class String
>    def all_chars? chars
>      if chars.empty?
>        empty?
>      else
>        /\A[#{chars}]*\z/ === self
>      end
>    end
> end
> 
> p 'foobar'.all_chars?('rabof')  # => true
> p 'foobar'.all_chars?('abc')    # => false
> p 'foobar'.all_chars?('')       # => false

Your method doesn't work, which can clearly be seen in these examples:

strs = ["aaa", "bbb", "ccc"]
chars = "abc"

strs.each do |str|

  if /\A[#{chars}]*/ =~ str
    print str, " - yes"
    puts
  else
    print str, " - no"
    puts
  end

end

--output:--
aaa - yes
bbb - yes
ccc - yes

It should be clear from the output that even though the string "aaa" 
passes your test, it is not true that all the characters in the string 
"abc"  appear in in the string "aaa".
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