From: "David A. Black" <dblack@...>
Date: 2009-10-03T02:59:04+09:00
Subject: Re: operating on a selection of objects

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Hi --

On Sat, 3 Oct 2009, Jes�s Gabriel y Gal�n wrote:

> On Fri, Oct 2, 2009 at 4:54 PM, James French
> <James.French@naturalmotion.com> wrote:
>> Hi,
>>
>> I want to be able to do operations to a selection of objects, something like this:
>>
>> class Config
>> �attr_accessor :name
>> end
>>
>> class ConfigSelection
>>
>> �def initialize(*configs)
>> � �@configs = configs
>> �end
>>
>> �def name=(n)
>> � �@configs.each{|c| c.name = n}
>> �end
>>
>> end
>>
>> a = Config.new
>> a.name = "a"
>>
>> b = Config.new
>> b.name = "b"
>>
>> s = ConfigSelection.new(a, b)
>> s.name = "s"
>>
>>
>> I was wondering if there might be a more elegant way of doing this, without having to explicitly duplicate all of Config's attributes in ConfigSelection?
>
> This is a way, with the restriction that it only checks instance
> methods defined in the class:
>
> irb(main):015:0> c = Config.new
> => #<Config:0xb7db3f78>
> irb(main):016:0> c.name="test"
> => "test"
> irb(main):017:0> c2 = Config.new
> => #<Config:0xb7dad038>
> irb(main):018:0> c2.name = "test2"
> => "test2"
>
> irb(main):041:0> class ConfigSelection
> irb(main):042:1> def method_missing meth, *args, &blk
> irb(main):043:2> if Config.instance_methods.include? meth.to_s
> irb(main):044:3> @configs.each {|c| c.send meth, *args, &blk}
> irb(main):045:3> else
> irb(main):046:3* super
> irb(main):047:3> end
> irb(main):048:2> end
> irb(main):049:1> end
> => nil
> irb(main):050:0> csel = ConfigSelection.new c,c2
> => #<ConfigSelection:0xb7d9c198 @configs=[#<Config:0xb7db3f78
> @name="test">, #<Config:0xb7dad038 @name="test2">]>
> irb(main):051:0> csel.name="changed"
> => "changed"
> irb(main):052:0> csel
> => #<ConfigSelection:0xb7d9c198 @configs=[#<Config:0xb7db3f78
> @name="changed">, #<Config:0xb7dad038 @name="changed">]>

While it's probably not likely, it is possible that you'll get some
false positives there. For example, if Config includes a module with a
method that ConfigSelection doesn't have, and then you call that
method on a ConfigSelection instance.... Like I said, not likely :-)
But it could happen. It's probably best at least to toss in a 'false':

   if Config.instance_methods(false)....

(but also beware that in 1.9, the *methods methods return arrays of
symbols).


David

-- 
David A. Black, Director
Ruby Power and Light, LLC (http://www.rubypal.com)
Ruby/Rails training, consulting, mentoring, code review
Book: The Well-Grounded Rubyist (http://www.manning.com/black2)
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