Re: Template Method Pattern (GoF) without abstract methods in Ruby

On Fri, Jan 11, 2019 at 4:08 AM Michael Schwarze <[email protected]>
wrote:

> Hi Austin,
>
> Thanks; I’m from a different programming language background and curious
> whether there is kind of a 'pattern of implementation‘ for implementing the
> Template Method Pattern in Ruby. My 'research‘ so far brought
> contra-dictionary results: the book on design patterns in Ruby saying not
> to use 'abstract‘ methods, but showing them in the respective examples and
> the examples found on the web |1, 2, 3] showing these 'abstract‘ methods in
> Ruby, too.
>

But that’s my point. If you’re trying to implement the `Template Method
Pattern`, you’re trying to use GoF as a recipe book. This is a mistake and
will only hinder your learning of Ruby. What problem are you actually
trying to solve? I have yet to see a place where I have needed to implement
most of the GoF patterns in Ruby—some of these are because the language
provides features that supplant the need for such a pattern. In Ruby, you
quite *literally* don’t need abstract methods.

class Processor
  def process
    step1
    step2
    step3
    finalize
  end

  private

  def finalize
    # finalize the process here
  end
end

class Foo < Processor
  private

  def step1; end
  def step2; end
  def step3; end
end

If I do Processor.new.process, I will get a NoMethodError because I have no
implementation of `step1`, `step2`, or `step3`. If I do `Foo.new.process`,
it works. You don’t need abstract methods in Ruby because the methods don’t
have to exist during compilation, because there’s no compilation phase or
static method resolution.

I don’t try to solve the template method pattern because I’ve been
developing long enough that I recognize that pattern descriptions are
forensic descriptions of common implementation patterns—often not necessary
in languages with advanced and/or functional features (they have
*different* patterns that can be forensically described) and not an
instruction manual or language comparison tool.

-a
-- 
Austin Ziegler • [email protected] • [email protected]
http://www.halostatue.ca/ • http://twitter.com/halostatue


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