From: Bulat Ziganshin <bulatz@...>
Date: 2002-11-11T23:46:33+09:00
Subject: Re: help with closure contexts

Hello t_gecks,

Monday, November 11, 2002, 5:25:50 PM, you wrote:

t> Question: Could you please explain to me why the context is copied
t> in the first case and not in the second ?

because variables holds only references to values. after you execute
"a=2" statement, aThing is not changed - it got it's value, reference
to 23 at the time of call. Try to reexecute "p1=nTimes(a)" after that
to get closure with new aThing

In the second example references to @a yields actual value of instance
variable. btw, try this code:

 def nTimes(aThing)
 return proc { |n| aThing * n }
 end

 a = "23"
 p1 = nTimes(a)
 puts p1.call(3)
 a << "4"
 puts p1.call(4)

 :)))

=>> code

t> # copy of the context for a closure

t> def nTimes(aThing)
t>       return proc { |n| aThing * n }
t> end

t> a = 23
t> p1 = nTimes(a)
t> puts p1.call(3)
t> a = 2
t> puts p1.call(4)

t> # versus reference to the context

t> class TestMe
t>      attr_reader :myProc
t>      def initialize()
t>          @myProc = proc { puts @a }
t>          @a = 0
t>      end
t>      def changeMember()
t>          @a = 2
t>      end
t> end

t> testMeFirst = TestMe.new
t> testMeFirst.myProc.call
t> testMeFirst.changeMember
t> testMeFirst.myProc.call

t> <= code

t> results in:

t> [bla@blub myTests]$ ruby test1.ruby
t> 69
t> 92
t> 0
t> 2




-- 
Best regards,
 Bulat                            mailto:bulatz@integ.ru