From: matt@... (matt neuburg)
Date: 2008-08-30T08:50:07+09:00
Subject: Re: assignment operator that treats empty and nil as the same thing

scooterm@hotmail.com <scooterm@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.

Would it suffice to subvert Hash in such a way that the value of an
element whose value is the empty string is reported as nil?

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

h = {"hey"=>"", "ho"=>"ha"}
h["hey"] ||= "homer"
p h

If that's too strong, you can devise your own function:

class Hash
  def set_if_empty(k,v)
    cur = self[k]
    if cur.nil? || cur == ''
      self[k] = v
    end
  end
end

h = {"hey"=>"", "ho"=>"ha"}
h.set_if_empty("hey", "homer")
p h



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