My Ruby Epiphany

Private methods in Ruby

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I’ve been using and teaching Ruby for many years now, but I recently had an epiphany about indentation.

I’ve long been annoyed by private and its lesser-used siblings protected and public because I saw them as “keywords” that change the context.

class Idea
  def example_public_method
    ...
  end

  private

  def example_private_method
    ...
  end
end

I’ve described it before as changing how the parser sees methods as it reads from the top down.

This never seemed very “Rubyish” to me. I had thought a block would make more sense:

class Idea
  def example_public_method
    ...
  end

  private do

    def example_private_method
      ...
    end

  end
end

But my recent epiphany made me realize I’ve been wrong the whole time:

private is to class and end as
else is to if and end.

Animation showing indentation of 'private'

if surprised?
  # do something
else
  # do something else
end

This also changes my mind in how we should indent it.

class Idea
  def example_public_method
    ...
  end

private

  def example_private_method
    ...
  end
end

I don’t know why it took me so many years to realize this. Anyone else with me?

About Daniel Morrison

Daniel founded Collective Idea in 2005 to put a name to his growing and already full-time freelance work. He works hard writing code, teaching, and mentoring.

Comments

Daniel Morrison
September 09, 2016 at 10:39 AM

This also means I disagree with what the community-built Ruby styleguide suggests but this is far from the first thing I’ve disagreed with.
chrismo
September 09, 2016 at 11:03 AM

I read else and rescue as alternate behavior, and private isn’t alternate behavior.
Daniel Morrison
September 09, 2016 at 11:16 AM

@chrismo: But I think it is different behavior. You’re defining methods as private instead of public. That’s a difference in how they behave.
Rob Cameron
September 09, 2016 at 20:16 PM

Yeah I’ve been doing that for years until 2.0 let you actually prefix def with it:

private def
…
end

No matter how far down the file you are you always know right away if the method is public or private.
Avdi Grimm
September 10, 2016 at 22:11 PM

I think it’s a tough adjustment for anyone who first encountered ‘public’ and ‘private’ in C** or Java. It was for me.

Now let me submit to you a third way of thinking about it:

‘public’ and ‘private’ are mode-switching commands sent to the class object.
Daniel Morrison
September 12, 2016 at 8:51 AM

@Avdi Grimm: I like that explanation, but is there anywhere else in Ruby that sort of thing happens? I can’t think of any.