Calling instance methods from within blocks

Question

I tried to implement a class allowing its subclasses to save method blocks for get them executed later. It work's, but it seems I took the wrong way. Have a look at this:

class SuperKlass  
  def self.exec_later(&block)
    @@block_for_later = block
  end

  def exec_now
    return unless @@block_for_later
    @@block_for_later.call
  end
end

class ChildKlass < SuperKlass
  exec_later do
    child_method
  end

  def child_method
    puts "Child method called"
  end
end

test_klass = ChildKlass.new
test_klass.exec_now

If I try to execute this piece of code, the call to child_method in the block results in a method-missing error. Does somebody know what I'm doing wrong, and what's the right way to add functionality like this?

Sony Santos · Accepted Answer · 2011-05-01 14:23:06Z

4

The block exec_later is running in the context of ChildKlass, not the instance test_klass. As child_method is an instance method, it isn't found on ChildKlass.

UPDATE: I found a solution:

  def exec_now
    return unless @@block_for_later
    instance_eval &@@block_for_later
  end

edited May 1, 2011 at 14:23

answered May 1, 2011 at 14:15

Sony Santos

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3 Comments

dhoelzgen Over a year ago

Great, this works. Allthough I knew about instance_eval, I didn't know that it can be used to execute a block with the ampersand. Thanks a lot for your answer!

Sony Santos Over a year ago

I am very happy to can help you, because I'm learning metaprogramming now, and I could use some of new knowledge with success. :) About the use of ampersand, I learned a lot of method/proc calls details here. I hope it can be useful to you, too.

dhoelzgen Over a year ago

This link really is helpfull for me, thank's again :) I found another link here which could probably helpful, about passing arguments if a block is called this way.

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