Ruby refinements with instance_eval

Question

I'd like to provide some refinements to a DSL. I'm able to get refinements working with this example:

module ArrayExtras
  refine Array do
    def speak
      puts 'array!'
    end
  end
end

module MyUniverse
  using ArrayExtras
  class Thing
    def initialize
      [1].speak
    end
  end
end
MyUniverse::Thing.new

This prints out "array!" just fine. But once I introduce instance_eval, the method can't be found:

module MyUniverse
  using ArrayExtras
  class DSL
    def initialize(&block)
      instance_eval(&block)
    end
  end
end

MyUniverse::DSL.new do
  [1].speak
end

I get a undefined methodspeak' for [1]:Array (NoMethodError)`

Is there a way to get refinements working within an instance_eval?

Jörg W Mittag · Accepted Answer · 2015-12-16 09:11:58Z

1

Refinements are lexically scoped. You are activating the Refinement in the wrong lexical context. You need to activate it where you are calling the refined method:

module ArrayExtras
  refine Array do
    def speak
      puts 'array!'
    end
  end
end

module MyUniverse
  class DSL
    def initialize(&block)
      instance_eval(&block)
    end
  end
end

using ArrayExtras

MyUniverse::DSL.new do
  [1].speak
end
# array!

answered Dec 16, 2015 at 9:11

Jörg W Mittag

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1 Comment

EugZol Over a year ago

So there is no way to make MyUniverse::DSL.new method call self-contained? I.e. to not require users of this method to add using ... line to their code.

Roland Studer · Accepted Answer · 2020-11-15 21:25:04Z

1

In some cases you can achieve it by using ArrayExtras on the binding.

module MyUniverse
  using ArrayExtras
  class DSL
    def initialize(&block)
      block.binding.eval("using ArrayExtras")
      instance_eval(&block)
    end
  end
end

MyUniverse::DSL.new do
  [1].speak
end

This will however only work if you are not using your class in an instance, it only works if the binding is a module or class context, otherwise the eval will fail because main.using is permitted only at toplevel .

answered Nov 15, 2020 at 21:25

Roland Studer

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Comments

sawa · Accepted Answer · 2015-12-16 08:00:44Z

-1

If you want to refine the ruby core BaseObject, you need to modify it as below.

module ArrayExtras
  refine ::Array do
    def speak
      puts 'array!'
   end
  end
end

It will be found in top level class.

edited Dec 16, 2015 at 8:00

sawa

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answered Dec 16, 2015 at 6:42

Auli

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