From: Gary Wright <gwtmp01@...>
Date: 2009-12-31T07:19:20+09:00
Subject: Re: Index of an array containing an instance, from this instance


On Dec 30, 2009, at 5:13 PM, Paul A. wrote:

> Hi,
> 
> If I do this:
> 
> class Foo
> end
> 
> my_array = []
> my_array[8] = Foo.new
> 
> ...From Foo instance, it is possible to get the array instance using
> self, such with:
> 
> Class Foo
>  def test
>    puts "the array is: #{self}"
>  end
> end
> 
> my_array[8].test # => the array is: (something like fooooobaaaar)
> 
> ...But is that possible to get its current indice (which is 8) where Foo
> is stored? In other words, how can I get the current indice of the array
> from Foo instance?


An object doesn't have any built-in notion of what other objects are referencing it.  In your example the array would have a reference to the Foo instance but the Foo instance doesn't automatically have any reverse reference to the array.  If you want/need that sort of thing you'll have to incorporate it into your implementation of Foo.

It is possible to search an array for a particular object and to return the index:

class Foo
end

my_array = []
instance = Foo.new

my_array[8] = instance
puts "index: #{my_array.index(instance)}"   # 8


Gary Wright