Yngve Hammersland Yngve Hammersland - 2 months ago 8
Ruby Question

How to access a (shadowed) global function in ruby

I was wondering how to access a global function

fn
in ruby from a class which also defined a method
fn
. I have made a workaround by aliasing the function like so:


def fn
end

class Bar
alias global_fn fn
def fn
# how to access the global fn here without the alias
global_fn
end
end


I'm looking for something along the lines of c++'s :: to access global scope but I can't seem to locate any information about it. I guess I don't know specifically what I'm looking for.

Answer

At the top-level a def adds a private method to Object.

I can think of three ways to get the top-level function:

(1) Use send to invoke the private method on Object itself (only works if the method is not a mutator since Object will be the receiver)

Object.send(:fn)

(2) Get a Method instance of the top-level method and bind it to the instance you want to invoke it on:

class Bar
  def fn
    Object.instance_method(:fn).bind(self).call
  end
end

(3) Use super (assumes no super classes of Bar below Object redefine the function)

class Bar
  def fn
    super
  end
end

UPDATE:

Since solution (2) is the preferable one (in my opinion) we can try to improve the syntax by defining a utility method on Object called super_method:

class Object
  def super_method(base, meth, *args, &block)
    if !self.kind_of?(base) 
      raise ArgumentError, "#{base} is not a superclass of #{self}" 
    end

    base.instance_method(meth).bind(self).call(*args, &block)
  end
end

Use like the following:

class Bar
  def fn
    super_method Object, :fn
  end
end

Where the first argument to super_method must be a valid superclass of Bar, the second argument the method you want to invoke, and all remaining arguments (if any) are passed along as parameters to the selected method.

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