From: Mike Gold <mike.gold.4433@...>
Date: 2009-01-23T14:25:03+09:00
Subject: Re: String doesnt auto dup on modification

RK Sentinel wrote:
> 
> - Do you keep freezing Strings you make in your classes to avoid
> accidental change
> 
> - Do you habitually dup() your string ?
> 

One possibility is copy-on-write.

require 'delegate'

class CopyOnWriteString < DelegateClass(String)
  DESTRUCTIVE_METHODS =
    String.public_instance_methods(false).grep(/!/).map(&:to_sym) +
    [
      :[]=,
      :<<,
      :concat,
      :initialize_copy,
      :replace,
      :setbyte,
      # ... and probably others ...
    ]

  DESTRUCTIVE_METHODS.each { |m|
    define_method(m) { |*args, &block|
      __setobj__(__getobj__.dup)
      __getobj__.send(m, *args, &block)
    }
  }
end

class Person
  def initialize(name)
    @name = name
  end
  def name
    CopyOnWriteString.new(@name)
  end
end

person = Person.new("fred")
name = person.name

p name        #=> "fred"
p person.name #=> "fred"

name << " flintstone"
p name        #=> "fred flintstone"
p person.name #=> "fred"

(I've used some 1.8.7+ only features.)
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