From: Phillip Gawlowski <cmdjackryan@...>
Date: 2008-05-02T05:24:47+09:00
Subject: Re: Please explain nuances of ||=

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Robert Klemme wrote:
| On 01.05.2008 20:54, Simon Krahnke wrote:
|> * David A. Black <dblack@rubypal.com> (18:56) schrieb:
|>
|>> Hi --
|>>
|>> On Fri, 2 May 2008, Ruby Freak wrote:
|>>
|>>> I am reading some of the ruby files in rails and I an seeing the ||=
|>>> method used a lot.
|>>> knowing ruby the way I do, I realize that she has lots of magical
|>>> surprises and I really want to get to know this girl!
|>> x ||= y means:  x || x = y
|>
|> No, it means: x = x || y
|
| I believe you are wrong.
|
| irb(main):001:0> h={}
| => {}
| irb(main):002:0> h=Hash.new true
| => {}
| irb(main):003:0> h[1]
| => true
| irb(main):004:0> h[1] ||= 10
| => true
| irb(main):005:0> h
| => {}
| irb(main):006:0>
|
| If you were right, h would look differently:
|
| irb(main):008:0> h=Hash.new true
| => {}
| irb(main):009:0> h[1] = h[1] || 10
| => true
| irb(main):010:0> h
| => {1=>true}
|
| The same topic has been discussed exhaustively a few days ago.
|
| Cheers
|
|     robert
|
|

You are wrong, too, though.

I refer you to Ruby-Talk 297145[0]:

Quoth Joshua Ballanco:
'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). '

x = x || 'a value' works when x is nil or false. Once the Hash has a
default value, it shouldn't be false, much less nil.

See:

irb(main):001:0> h = Hash.new
=> {}
irb(main):002:0> h[1].nil?
=> true
irb(main):003:0> h[1] = h[1] || 10
=> 10
irb(main):004:0> h[2] = 'not nil'
=> "not nil"
irb(main):005:0> h[2] = h[2] || 'a value'
=> "not nil"
irb(main):006:0> h[3] = false
=> false
irb(main):007:0> h[3] = h[3] || 'not false'
=> "not false"

[0] http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/297145

- --
Phillip Gawlowski
Twitter: twitter.com/cynicalryan
Blog: http://justarubyist.blogspot.com

~   Calvin: I'm a genius, but I'm a misunderstood genius.  Hobbes: What's
misunderstood about you?  Calvin: Nobody thinks I'm a genius.  -- Calvin
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