From: RichardOnRails <RichardDummyMailbox58407@...>
Date: 2008-08-30T12:00:05+09:00
Subject: Re: assignment operator that treats empty and nil as the same thing

On Aug 29, 10:21 pm, RichardOnRails
<RichardDummyMailbox58...@uscomputergurus.com> wrote:
> On Aug 29, 6:01 pm, "scoot...@hotmail.com" <scoot...@hotmail.com>
> wrote:
>
>
>
> > ### test1
> > otest   =   {};
> > otest['first_name'] ||= 'homer';
> > puts otest.inspect;
>
> > ### test2
> > otest   =   {'first_name'=>''};
> > otest['first_name'] ||= 'homer';
> > puts otest.inspect;
>
> > Problem: test1 produces the correct output, but test2 produces
> > unwanted output (the value remains as an empty string). I realize that
> > ruby treats the empty string as "true" ... nevertheless I want to find
> > an assignment operator in ruby that treats nil and empty exactly the
> > same way, with the behavior shown in test1.
>
> > Question: Is there a way to do this in ruby *without* resorting to an
> > if statement or some other construct such as:
>
> > otest['first_name'] = (otest['first_name'].empty?) 'homer' :
> > otest['first_name'];
>
> > I would like to handle this with a *single* assignment operator, just
> > like you can do in test1.
>
> The problem is that you think that otest['first_name] is nil in both
> tests when you try the conditional assignment.  As the following code
> shows it's only nil the first time;  the second time it's (an empty)
> String.
>
> otest   =   {};
> puts otest['first_name'] .class.to_s
> otest['first_name'] ||= 'homer';
> puts otest.inspect;
>
> ### test2
> otest   =   {'first_name'=>''};
> puts otest['first_name'] .class.to_s
> otest['first_name'] ||= 'homer';
> puts otest.inspect;
>
> HTH,
> Richard

Maybe I can redeem myself: Matt gave you a great solution in reopening
the Hash definition.  I recommend a minor improvement as follows:

class Hash
  alias_method "orig_fetch", "[]"
  def [](what)
      result = orig_fetch(what)
      result = nil if result == ''
  end
end

### test1
otest   =   {}
otest['first_name'] ||= 'homer'
puts otest.inspect  #= {"first_name"=>"homer"}

### test2
otest   =   {'first_name'=>''}
otest['first_name'] ||= 'homer'
puts otest.inspect  #= {"first_name"=>"homer"}

HTH,
Richard