From: Matt Gretton <matthew.gretton@...>
Date: 2007-05-20T20:32:14+09:00
Subject: Re: Calling a block with parameters in a new scope

Matt Gretton wrote:
> Ruby Talk wrote:
>> Calling a block in a new scope is easy enough:
>> 
>> self.instance_eval &block
>> 
>> And calling a block, passing it parameters is easy enough:
>> 
>> block.call(*params)
>> 
>> But is there some way to do both? To both change the scope of evaluation
>> and pass variables into the block.
> 
> Hello,
> 
> I'm not sure I fully understand the question being asked here. Can you 
> provide a small bit of code to highlight what you are trying to acheive.
> 
> Do you wish to pass vaiables into the instance_eval block?
> 
> Any variables in scope when the instance_eval block is called can be 
> used in the instance_eval block itself. However, if you were to pass a 
> proc object into the instance_eval it would retain the context it was 
> created at.
> 
> See below for an example of this.
> 
> class Test
>   def initialize(arg)
>     @instance_variable = arg
>   end
> end
> 
> test_obj = Test.new("initializing_arg")
> 
> outside = "outside instance_eval"
> 
> proc = Proc.new {|arg| puts self} #self main here
> 
> test_obj.instance_eval do
>    puts @instance_variable #test_obj instance variable.
>    puts outside   #any variable from outside the block can be passed in.
>    puts proc #will return main rather than the object
> end
> 
> Hmm, I get the feeling I have ranted about stuff that does not help you 
> one bit with your question...
> 
> Get back to me with a bit more detail and hopefully I'll be able to 
> help!
> 
> Cheers,
> 
> Matt.


Oops, that last 'puts proc' should be proc.call("whatever")

If full:

class Test
  def initialize(arg)
    @instance_variable = arg
  end
end

test_obj = Test.new("initializing_arg")

outside = "outside instance_eval"

proc = Proc.new {|arg| puts self} #self main here

test_obj.instance_eval do
   puts @instance_variable #test_obj instance variable.
   puts outside   #any variable from outside the block can be passed in.
   proc.call("whatever") #will return main rather than the object
end


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