Issue #7747 has been updated by 11 22.


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Feature #7747: Expanded API for Binding semantics
https://bugs.ruby-lang.org/issues/7747#change-53324

* Author: Joshua Ballanco
* Status: Open
* Priority: Normal
* Assignee: 
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=begin
Currently, the only way to create a new instance of Binding is to get a copy of the current scope's binding, or ask some other object for its binding.In either case, the binding object returned always has semantics identicalto the original binding. In other words, a binding object used with eval is capable of (not necessarily an exhaustive list):

* redefining methods on the binding target
* defining new methods on the binding target
* getting/setting instance variables
* getting/creating new constants

This feature proposal would introduce a new mechanism for creating a binding and adjusting its relationship with the source binding. For example, if you have a class (({Foo})) defined like so:

    class Foo
      def say
        puts "hello!"
      end
    end

Then you would be able to create a new binding that ((*won't*)) propagate new definitions to the parent binding like so:

    new_binding = Binding.new(Foo)
    new_binding.propagate = false
    new_binding.eval("def shout; puts 'HI!'; end")
    
    Foo.new.say #=> "hello!"
    Foo.new.shout #=> No Method Error
    new_binding.eval("Foo.new.say") #=> "hello"
    new_binding.eval("Foo.new.shout") #=> "HI!"

If, additionally, we introduce a way to merge or combine bindings, then this API could actually be used to implement refinements in pure Ruby like so (note I am also assuming that (({Binding#eval})) gains the ability to take a block):

    class Module
      def refine(klass, &block)
        @refined_bindings ||= {}
        refinement_binding = Binding.new(klass)
        refinement_binding.propagate = false
        refinement_binding.shadow = true
        refinement_binding.eval &block
        (@refined_bindings[self.name] ||= []) << refinement_binding
      end
    
      def using(mod)
        @refined_bindings[mod].each { |refinement| self.binding.merge(refinement) }
      end
    end

Following is the preliminary list of additional APIs I am tentatively proposing (though I expect this to change with additional discussion):

* (({Binding.new(an_object)})) - creates a new Binding object that "inherits" the binding of the argument; essentially equivalent to (({an_object.send(:binding).dup}))
* (({Binding#propagate}))/(({Binding#propagate=})) - boolean; determines whether new method, class, or Constant defs are propagated into the "parent" binding's scope
* (({Binding#shadow}))/(({Binding#shadow=})) - boolean; sets whether or not new values for existing methods/constants/variables can be set
* (({Binding#freeze})) - causes the Binding to capture all existing methods/constants/variables in scope at call time, and "disconnect" from the parent binding, so that any updates to definitions or values are no longer reflected into the "child" binding
* (({Binding#merge(other_binding)})) - combines the method/constant/variable bindings in (({other_binding})) with the receiver; effectively shadows the "parent" of (({other_binding})) within the receiver binding
=end




-- 
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