From: Michael Neumann <mneumann@...>
Date: 2004-08-18T09:27:39+09:00
Subject: Re: Getting the binding of the caller

Florian Gross wrote:
> Michael Neumann wrote:
> 
>> Thanks for the quick answer... uhm, but it does seem to behave as it 
>> should:
>>
>>   require 'binding_of_caller'
>>   class A
>>     def m
>>       Binding.of_caller do |binding|
>>         eval("self", binding)
>>       end
>>     end
>>   end
>>
>>   p A.new.m # => #<A:0x8115a14>
>>
>> I expect "self" to be "main".
> 
> 
> That's weird -- can't find an explanation for it, because the following 
> works:
> 
> require 'binding_of_caller'
> this = self
> class A
>   def m
>     Binding.of_caller do |binding|
>       eval("this", binding)
>     end
>   end
> end
> 
> p A.new.m # => main
> 
> Maybe somebody has the knowledge needed to explain what's going on there?

Hm, it still doesn't work in my special case, as I get a
"Binding.of_caller used in non-method context or trailing statements of 
method using it aren't in the block." exception (and I really don't 
understand how this Binding.of_caller really works ;-):

require 'binding_of_caller'

class Decorator
   def initialize(&block)
     @block = block
   end

   def >>(meth_id)
     obj = Binding.of_caller do |binding|
       eval("this", binding)
     end
     old = method(meth_id)
     new = @block.call(old)

     # the line below is why I need the Binding.of_caller
     obj.class.send(:define_method, meth_id, new)
   end
end

def wrapwith(value)
   Decorator.new {|old|
     proc {|*args|
       print "##", value, "\n"
       old.call(*args)
     }
   }
end

wrapwith(42) >>
def f(x) x * 2 end

p f(4)

##############

Regards,

   Michael