If `self` is always the implied receiver in Ruby, why doesn't `self.puts` work?

Question

In Ruby, my understanding is that self is the implied receiver for any bare method call. However:

~: irb
>> puts \"foo\"
foo
=> nil
>         


        

Answer 1

Because that's the definition of privacy in Ruby: private methods can only be called with an implicit receiver.

Actually, there's an exception to this rule: because foo = bar always creates a local variable, you are allowed to call private setters like self.foo = bar, because otherwise you wouldn't be able to call them at all (without using reflection).

Answer 2

Private methods can't have a receiver

I think the answer is this: Ruby's way of enforcing method privacy is that it doesn't allow calling private methods with an explicit receiver.

An example:

class Baker
  def bake_cake
    make_batter
    self.use_oven # will explode: called with explicit receiver 'self'
  end

  private
  def make_batter
    puts "making batter!"
  end

  def use_oven
    puts "using oven!"
  end

end

b = Baker.new
b.bake_cake

Since there can be no explicit receiver, you certainly can't do b.use_oven. And that is how method privacy is enforced.

Answer 3

You're correct that self is the implied receiver when you don't specify one explicitly. The reason that you're not allowed to do self.puts is that you may not call private methods with an explicit receiver (even if that receiver is self) and as the error message says, puts is a private method.

Answer 4

You can't access private methods in ruby using the self. syntax, or generally speaking using any receiver (something in front of the .). That is only possible for protected methods.