Ruby class class without inheritance

Question

I just did this experiment:

class A < Hash
  def foo
    'foo'
  end
end

class A < Hash
  def bar 
    'bar'
  end
end

As long as I get the expected result, the second declaration extends the first. However, I was surprised by this:

class A
  def call
    puts foo
    puts bar
  end
end

The above code works, but only if I declare it later. Otherwise, I get:

TypeError: superclass mismatch for class A

Can I assume that it is safe in Ruby to skip a superclass specification without side effects after making sure that the original-first declaration has been parsed?

Answer 1

You can declare inheritance only at the first appearance after the class definition, so the options below will work:

• If you defined the same class inheritance:

  class A < Hash
  end
  
  class A < Hash
  end
  

• , undefined inheritance:

  class A < Hash
  end
  
  class A
  end
  

• , Object class:

  class A
  end
  
  class A
  end
  

:

• , :

  class A
  end
  
  class A < Hash
  end
  
  TypeError: superclass mismatch for class A
  

• ( String) , ( Hash):

  class A < String
  end
  
  class A < Hash
  end
  
  TypeError: superclass mismatch for class A
  

Answer 2

@ , . .

:

class A
  def call
    puts foo
    puts bar
  end
end

, , Module#class_eval:

, , , , / . . module_eval .

A.class_eval do
  def _call
    puts foo
    puts bar
  end
end