From: Gavin Kistner <gavin@...>
Date: 2005-06-03T12:24:54+09:00
Subject: Re: Implementing a Read-Only array

--Apple-Mail-1--124546398
Content-Transfer-Encoding: 7bit
Content-Type: text/plain;
	charset=US-ASCII;
	delsp=yes;
	format=flowed

On Jun 2, 2005, at 4:54 PM, Ara.T.Howard wrote:
> On Fri, 3 Jun 2005, Gavin Kistner wrote:
>> However...if I've undef'd #[]=, then that won't work, right?
> but that means that not even you can mutate it.  if not even you  
> can mutate it
> why not just use Object#freeze?

Well, if I alias it first I can. (This is using my original non- 
delegated method, since the delegator technique (as I've currently  
implemented it) does allow the custom mutator method to affect the  
wrapped object directly.

class Array
     def mutate(k,v); self[k]=v; end
end

class ImmutableArray < Array
     alias_method :'__ro_[]=', :'[]='
   %w{
     << []= clear concat delete delete_at delete_if fill
     flatten! insert map! pop push reject! replace
     reverse! shift slice! sort! uniq! unshift
   }.each{ |m|
         undef_method( m )
     }
end

ro = ImmutableArray.new( [0,1,2] )

ro.send( :'__ro_[]=', 1, 'one' )
p ro
#=> [0, "one", 2]

ro.mutate( 2, 'two' )
#=> /Users/gavinkistner/Desktop/readonlyarray.rb:11:in `mutate':  
undefined method `[]=' for [0, "one", 2]:ImmutableArray (NoMethodError)
     from /Users/gavinkistner/Desktop/readonlyarray.rb:44


--Apple-Mail-1--124546398--