From: Daniel Finnie <danfinnie@...>
Date: 2006-12-17T07:59:53+09:00
Subject: Re: Just some Ruby language ideas, comments wanted.

I did something like that for the current Ruby Quiz, but it doesn't do 
the []=, which I think is cool.  The code is a bit shorter though:
class ArrayValue
   instance_methods.each do |m|
     undef_method(m) unless m =~ /^_*(method_missing|send|id)_*$/
   end

   def initialize(origArray, origIndex)
     @origArray, @origIndex = origArray, origIndex
   end

   def set(newObj)
     @origArray[@origIndex] = newObj
   end

   def get
     @origArray[@origIndex]
   end

   def method_missing(method, *args)
       get.send(method, *args)
     rescue
       super
   end
end

class Array
   def to_av()
     ret = []
     each_index {|x| ret << ArrayValue.new(self, x) }
     ret
   end
end

Sample usage:
daniel@daniel-desktop:~$ irb -r 'arrayvalue.rb'

irb(main):001:0> ary = [1, 2, 3, 4, "SomeString", :ASymbol]
=> [1, 2, 3, 4, "SomeString", :ASymbol]

# Set the first String to 42.
irb(main):002:0> ary.to_av.find{|x| x.kind_of?(String)}.set(42)
=> 42

# Changes are reflected in the original array.
irb(main):003:0> ary
=> [1, 2, 3, 4, 42, :ASymbol]

# Set the 3rd Numeric value to 43
irb(main):004:0> ary.to_av.select{|x| x.kind_of?(Numeric)}[2].set(43)
=> 43

# Changes are reflected in the original array.
irb(main):005:0> ary
=> [1, 2, 43, 4, 42, :ASymbol]

Logan Capaldo wrote:
> On Sun, Dec 17, 2006 at 04:00:49AM +0900, Devin Mullins wrote:
>> Daniel Finnie wrote:
>>> How this would work:
>>> Currently, the following would default to "i" if the element doesn't exist.
>>> [4, 6, 9].fetch(4, "i")
>>> This would do the same thing:
>>> [4, 6, 9][4].default("i") or [4, 6, 9].fetch(4).default("i")
>> I get along fine with:
>>   [4, 6, 9].fetch(4)||'i'
>>
>> Sure, it has false misses on instances of FalseClass, but I live with 
>> the pain. Besides, what if the above array contained nil?
>>
>>> This would allow things like:
>>> ary = [4, nil, 6, nil]
>>> ary.select{|x| x.nil?}[1].set(2)
>>> ary # => [4, nil, 6, 2]
>> May I suggest:
>>   ary.select{|x| x.nil?}[1] = 2
>> as a better interface.
>>
>> = isn't overridable, but []= is.
>>
>> I see more potential in your second thing... Build it as a stand-alone 
>> Ruby library first.
>>
>> Devin
> Here, I'll evenget you started:
> 
> % cat view.rb
> class ArrayView
>   class ArrayIndexRef
>     def initialize( array, index )
>       @array = array
>       @index = index
>     end
> 
>     def value
>       @array[@index]
>     end
> 
>     def value=(new_value)
>       @array[@index] = new_value
>     end
>   end
> 
>   def initialize( array )
>     @array = array
>     @references = []
>   end
> 
>   def [](*args)
>     if args.length == 1 and args.kind_of? Range or args.length > 1
>       @references[*args].map { |x| x.value }
>     else
>       @references[*args].value
>     end
>   end
> 
>   def []=(index, value)
>     @references[index].value = value
>   end
> 
>   def each
>     @references.each do |x|
>       yield x.value
>     end
>   end
> 
> 
>   def add_ref( index )
>     @references << ArrayIndexRef.new( @array, index )
>   end
> end
> 
> 
> class Array
>   def select_view
>     r = ArrayView.new( self )
>     each_with_index do |item, index|
>       r.add_ref( index ) if yield( item ) 
>     end
>     r
>   end
> end
> 
> a = (1..10).to_a
> 
> p a
> b = a.select_view { |x| (x % 2).zero? }
> b[0] = 42
> p a
> 
> % ruby view.rb
> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
> [1, 42, 3, 4, 5, 6, 7, 8, 9, 10]
> 
>