From: Robert Dober <robert.dober@...>
Date: 2008-04-05T21:24:43+09:00
Subject: Re: The ||= assignment operator

On Sat, Apr 5, 2008 at 10:25 AM, Peņa, Botp <botp@delmonte-phil.com> wrote:
> From: Joshua Ballanco [mailto:jballanc@gmail.com]
>  # Not at all. Rather, this is just a subtle misunderstanding of
>
> # how hash is implemented. Consider the following:
>  # >> h = Hash.new
>  # => {}
>  # >> h[:test] ||= 'testing without default'
>  # => "testing without default"
>  # >> h
>  # => {:test=>"testing without default"}
>  # >> h = Hash.new('default value')
>  # => {}
>  # >> h[:test] ||= 'testing with default'
>  # => "default value"
>  # >> h
>  # => {}
>  # The only reason that Chris' example behaves like "x || x = stuff" is
>  # because he's defined a default value for the hash. If you set
>  # a default value, than you'll never have a keyed value be empty
>  # (i.e. nil). Consider further:
>  # >> h = Hash.new
>  # => {}
>  # >> puts 'empty' unless h[:test]
>  # empty
>  # => nil
>  # >> h = Hash.new('default value')
>  # => {}
>  # >> puts 'empty' unless h[:test]
>  # => nil
>
>  my question is simple,
>
>  given,
>
>
>  h = Hash.new('default value')
>  #=> {}
>
>  why is
>
>  h[:test] ||= 'this is alternative'
>  #=> "default value"
>  h
>  #=> {}
>
>  different from
>
>  h[:test] = h[:test] || 'this is alternative'
>  #=> "default value"
>  h
>  #=> {:test=>"default value"}
>
>  ??
>
>  That is not a nice surprise, imho; and the (syntax) sugar is not sweet :)
>
>  kind regards -botp
>
>
I respectfully disagree, this is very well defined behavior, I
partially blame the list which *very* often explained to newbies that

@x ||= value

assignes value to @x when it was not defined before. It is sad that
things are incorrectly explained, that is all.
Furthermore things are simple

(1) lval ||= rval  is lval = lval || rval
(2) nil || x = x
(3) false || x = x
(4) non initialized ivars evaluate to nil

once one accepts these basic rules of the language there is no surprise.
I like the syntactic sugar but to use a recently used quote "DE
GVSTIBVS NON DISPVTANDVM EST"

Cheers
Robert


-- 
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---
Whereof one cannot speak, thereof one must be silent.
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