From: Wilson Bilkovich <wilsonb@...>
Date: 2007-01-15T06:02:36+09:00
Subject: Re: checking if a string matches a regexp - am I missing something?

On 1/14/07, Rob Sanheim <rsanheim@gmail.com> wrote:
> On 1/13/07, William James <w_a_x_man@yahoo.com> wrote:
> > Rob Sanheim wrote:
> > > On 1/13/07, James Edward Gray II <james@grayproductions.net> wrote:
> > > > On Jan 13, 2007, at 9:43 PM, Rob Sanheim wrote:
> > > >
> > > > > I figure that I must be missing something really obvious with this
> > > > > question.  But here goes:
> > > > >
> > > > > I want to know if a string matches a regular expression.  I don't care
> > > > > where the match begins, I don't want a matchdata object, I don't want
> > > > > to check for nil, I just want a boolean indicating if a string matches
> > > > > a regexp.  And I want this to be one method call.  From what I can
> > > > > tell, this is the closest I can get:
> > > > >
> > > > > ("string" =~ reg) >= 0 # ugly
> > > >
> > > > Just drop the noise:
> > > >
> > > > "string" =~ reg # => int results are +true+ and nil is +false+
> > > >
> > > > Hope that helps.
> > > >
> > >
> > > True...but here is a cleaned up version of the place where I tried to do that:
> > >
> > >  def valid_query?
> > >  # query is a string accessor
> > >     if query_is_plain_text?
> > >       is_valid = valid_query_length? && (query =~ regex)
> > >     else
> > >       is_valid = query_is_url?
> > >     end
> > >     is_valid
> > >   end
> > >
> > > So of course, when it was both a valid query and had a valid length,
> > > it would return zero because it matched the start of the regexp.  The
> > > caller of the method wanted true or false only, not zero.
> >
> > Who wrote a caller that wanted true or false only, and why?
> > What does the caller do when it receives 0?
> >
> > irb(main):002:0> puts 'yeah' if true
> > yeah
> > => nil
> > irb(main):003:0> puts 'yeah' if 0
> > yeah
> > => nil
> > irb(main):004:0> puts 'yeah' if false
> > => nil
> >
> > If you actually have a caller written so mindlessly that it
> > only works with true or false:
> >
> >     !!(is_valid = valid_query_length? && (query =~ regex) )
>
> Well I guess I was mindless, then.  =)  I wrote a spec that was using
> "should.be(true)" and "should.be(false)", which is using assert_same
> underneath, so of course it was failing if it returned 0.  So the easy
> solution is to use should.equal instead of should.be.  Thanks for the
> double !! tip, though.
>
> Now, about allowing regexp's for "include?" - doesn't that fit well
> with the humane interface of String?

If you are using RSpec, you can simply say:
"blah".should =~ /ah/
or
"blah".should_not =~ /z/

If you want "include? with a Regexp" behavior, you can do:
if some_string[/some pattern/]