From: "Peña, Botp" <botp@...>
Date: 2008-04-05T17:25:46+09:00
Subject: Re: The ||= assignment operator

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