From: Todd Benson <caduceass@...>
Date: 2008-05-09T09:14:56+09:00
Subject: Re: Doing an AND in regexp char class

On Thu, May 8, 2008 at 7:00 PM, Joel VanderWerf <vjoel@path.berkeley.edu> wrote:
> Todd Benson wrote:
>>
>> On Thu, May 8, 2008 at 6:07 PM, ara.t.howard <ara.t.howard@gmail.com>
>> wrote:
>>>
>>> On May 8, 2008, at 3:40 PM, Todd Benson wrote:
>>>>
>>>> This question arises out of a couple of recent threads and may or may
>>>> not be a Ruby-specific question.
>>>>
>>>> I can check with a character class if one of the characters in the
>>>> class exists or does not exist, but can I use a regexp to check if a
>>>> string absolutely contains all of the characters in the class?
>>>>
>>>> Using a set perspective, I can do it like this in irb...
>>>>
>>>> s1 = "hello there"
>>>> s2 = "ohi"
>>>> (s2.unpack('c*') & s1.unpack('c*')).size == s2.size
>>>>
>>>> => false
>>>>
>>>> I use unpack to avoid creating a bunch of String objects, one for each
>>>> element in the array, which would happen if I used #split.  What I'm
>>>> wondering is if there is a way to do this with a simple regexp.
>>>>
>>>> Thanks,
>>>> Todd
>>>
>>> cfp:~ > cat a.rb
>>> class String
>>>  def all_chars? chars
>>>   tr(chars, '').empty?
>>>  end
>>> end
>>>
>>> p 'foobar'.all_chars?('rabof')
>>> p 'foobar'.all_chars?('abc')
>>> 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

I'm drawing a blank here with this one.  Why doesn't this work then...

irb(main):006:0> r = /\A[oh]*\z/
=> /\A[oh]*\z/
irb(main):007:0> s = "hello, there"
=> "hello, there"
irb(main):008:0> r === s
=> false

Todd