From: Gavin Kistner <gavin@...>
Date: 2005-06-02T23:46:50+09:00
Subject: Re: Implementing a Read-Only array

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On Jun 2, 2005, at 3:55 AM, Robert Klemme wrote:
> You don't even need the variable and the ugly concat
> [...]

Prettier, to be sure.


Now I'm bothered by the fact that my delegate array thinks that it  
responds to methods which only exist to raise an error. I've hacked  
the delegate.rb code to add an #undelegate_method method. Comments on  
the code I used (and a cleaner way to do it) would be appreciated.  
Does this (feature, if not implementation) seem like it might be a  
good addition to the standard lib code?



[Slim:~/Desktop] gavinkis% diff /usr/local/lib/ruby/1.8/delegate.rb / 
usr/local/src/ruby-1.8.2/lib/delegate.rb
100,110d99
<     def self._ignored_methods
<       @_ignored_methods ||= {}
<     end
<     def self.undelegate_methods( *methods )
<       ignore = _ignored_methods
<       methods.flatten.each do |m|
<         m = m.to_s.intern
<         undef_method( m )
<         ignore[ m ] = true
<       end
<     end
115d103
<       super if self.class._ignored_methods[ m ] #raise  
StandardError, "No such method: #{name}"

[Slim:~/Desktop] gavinkis% cat readonlyarray.rb
require 'delegate'
class ReadOnlyArray < DelegateClass( Array )
   undelegate_methods( %w{
     << []= clear concat delete delete_at delete_if fill
     flatten! insert map! pop push reject! replace
     reverse! shift slice! sort! uniq! unshift
   } )
end

a = [1,2]
ro = ReadOnlyArray.new( a )
a << 3

puts a.respond_to?( :concat )
puts ro.respond_to?( :concat )
a.concat( [4,5,6] )
ro.concat( [7,8,9] )

[Slim:~/Desktop] gavinkis% ruby readonlyarray.rb
true
false
/usr/local/lib/ruby/1.8/delegate.rb:115:in `method_missing':  
undefined method `concat' for [1, 2, 3, 4, 5, 6]:ReadOnlyArray  
(NoMethodError)
         from readonlyarray.rb:17


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