Forum: Ruby binding in ruby1.9

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Tim P. (Guest)
on 2009-01-30 20:32
(Received via mailing list)
Could someone explain why this code does not work in ruby1.9 and
possibly provide a workaround. The end goal is to be able to pass a
binding to an ERb result method that provides a limited set of
variables to the ERb template evaluation.

 > cat a.rb

obj = Object.new
class << obj
   attr_accessor :foo
end
obj.foo = 'the foo method'
eval "puts foo", obj.__send__(:binding)

 > ruby a.rb
the foo method

 > ruby1.9 a.rb
a.rb:7:in `eval': undefined local variable or method `foo' for
main:Object (NameError)
  from a.rb:7:in `eval'
  from a.rb:7:in `<main>'

 >ruby1.9 --version
ruby 1.9.1p0 (2009-01-30 revision 21907) [i386-darwin9.6.0]



Blessings,
TwP
Charles Oliver N. (Guest)
on 2009-01-30 22:00
(Received via mailing list)
Tim P. wrote:
> end
> obj.foo = 'the foo method'
> eval "puts foo", obj.__send__(:binding)

What an unusual feature to keep coming up.

The contract of binding is that it returns a reification of the caller's
binding. Under 1.8, however, the behavior acted a bit differently, using
the "self" that binding was actually called against. 1.9 has largely
remedied this by always returning the binding of the caller, even if you
__send__(:binding) to another object.

I believe instance_evaling "binding" against the target object would
give you the behavior you're looking for:

[headius @ cnutter:~/projects/ruby-benchmark-suite]
â—† ruby -e "o = Object.new; p o; eval 'p self', o.__send__(:binding)"
#<Object:0x29414>
#<Object:0x29414>
[headius @ cnutter:~/projects/ruby-benchmark-suite]
â—† ruby1.9 -e "o = Object.new; p o; eval 'p self', o.__send__(:binding)"
#<Object:0x3e736c>
main
[headius @ cnutter:~/projects/ruby-benchmark-suite]
â—† ruby1.9 -e "o = Object.new; p o; eval 'p self',
o.instance_eval{binding}"
#<Object:0x3e72a4>
#<Object:0x3e72a4>

- Charlie
Tim P. (Guest)
on 2009-01-30 22:22
(Received via mailing list)
On Jan 30, 2009, at 12:56 PM, Charles Oliver N. wrote:

>> obj.foo = 'the foo method'
>
Okay, that explanation makes sense. My new implementation (following
along with the Kernel docs)

 > cat a.rb
obj = Object.new
class << obj
   attr_accessor :foo
   def get_binding() binding; end
end
obj.foo = 'the foo method'
eval "puts foo", obj.get_binding

 > ruby1.9 a.rb
the foo method


Thanks for the insight.

Blessings,
TwP
Charles Oliver N. (Guest)
on 2009-01-30 23:16
(Received via mailing list)
Tim P. wrote:
> eval "puts foo", obj.get_binding
>
>  > ruby1.9 a.rb
> the foo method

Even better!

- Charlie
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