Inheritance scenario in Ruby

Question

I have the following code in Ruby:

class Base
  def Function1
    puts 'Base Function1'
  end

  def Function2
    Function1
  end
end

class Derived < Base
  def Function1
    puts 'Derived Function1'
  end
end

obj = Derived.new
obj.Function2

When I run the above code, I get the following error:

/Users/vkuppuswamy/.rvm/rubies/ruby-2.0.0-p0/bin/ruby -e $stdout.sync=true;$stderr.sync=true;load($0=ARGV.shift) /Users/vkuppuswamy/RubymineProjects/TestRubyProj/TestRuby.rb
/Users/vkuppuswamy/RubymineProjects/TestRubyProj/TestRuby.rb:7:in `Function2': uninitialized constant Base::Function1 (NameError)
    from /Users/vkuppuswamy/RubymineProjects/TestRubyProj/TestRuby.rb:18:in `<top (required)>'
    from -e:1:in `load'
    from -e:1:in `<main>'

I can see that the in Function2 in class Base, an attempt has been made to call some constant Function1. I do not see why this would happen. I thought the derived class Function1 method will be invoked. When I change the Function2 in the base class to:

  def Function2
    self.Function1
  end

where I invoke Function1 using self, it works, and I get in output:

Derived Function1

Can you please help me understand why this is happening. I thought the self was implicit in Ruby.

Conventions in Ruby are that Constants start with a Capital letter, while methods are lowercase. Try calling your functions function1 etc. What happens? — Thomas Klemm
– Thomas Klemm, Commented Jun 13, 2013 at 7:19

Patrick Oscity · Accepted Answer · 2013-06-13 07:30:32Z

5

Constants (this includes classes) are written in UpperCase, methods/functions are written in lowercase. This has nothing to do with inheritance, consider:

def Foo
  puts 'Foo'
end

Foo
# NameError: uninitialized constant Foo

This happens because when Ruby sees an uppercase token, it looks for a constant and that's it. You could explicitly tell Ruby to look for a method by using parentheses () but just don't do it:

Foo()
# Foo

Use lowercase method names instead. Then, your code will work as expected:

class Base
  def function1
    puts 'Base function1'
  end

  def function2
    function1
  end
end

class Derived < Base
  def function1
    puts 'Derived function1'
  end
end

obj = Derived.new
obj.function2

This prints

Derived function1

edited Jun 13, 2013 at 7:30

answered Jun 13, 2013 at 7:24

Patrick Oscity

54.9k19 gold badges149 silver badges173 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Inheritance scenario in Ruby

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related