Question

How I can create/extract a variable/hash into the current binding in Ruby?
For instance, the following results in a NameError:

class Hash
  def extract(b)
    self.each do |key, value|
      bind = b.eval <<-END
        #{key} = nil
        proc { |value| #{key} = value }
      END
      bind.call(value)
    end
  end
end

hash = {:a => 1}
hash.extract(binding)
puts a

Noteworthy mentioning, each call to Kernel#binding returns a different
Binding object instance, which makes me think that I’m not really changing
the binding of the caller of Hash#extract. For instance, the following
works:

class Hash
  def extract(b)
    self.each do |key, value|
      bind = b.eval <<-END
        #{key} = nil
        proc { |value| #{key} = value }
      END
      bind.call(value)
    end
  end
end

hash = {:a => 1}
b = binding
hash.extract(b)
eval('puts a', b)

Answer 1

I’m unsure how make local variables appear within the execution context of the caller after the current binding has been passed to a method (e.g., #export_to, below). But something similar can be done that will superficially achieve the same effect:

class Hash
  def export_to(o)
    each do |key, value|
      o.define_singleton_method(key) { value }
    end
  end
end

hash = {:a => 1}
hash.export_to self
puts a

Note that self is being passed rather than binding.

Also note that a common pattern here is to set instance variables rather than methods, in which case puts and later code would now be able to reference @a.