A simple pointer class

description.md

Pointer class

Motivation:

Using #tap to operate on and return a value is a useful technique for clean code in Ruby. However, sometimes the value you want to return changes, or you don't even know it at the start. In those cases, you can't use #tap.

This Pointer class defines a #tapp method. #tapp takes a block, just like tap. However, the pointer yielded to the block can be assigned and reassigned using <=, and that assigned value is what is returned from #tapp, not the pointer itself.

pointer.shard.rb

class Pointer

  ##############
  #            #
  # Initialize #
  #            #
  ##############
  
  def initialize(obj = nil)
    @object = obj
  end

  #############
  #           #
  # Operators #
  #           #
  #############
  
  def <=(obj)
    @object = obj
  end

  def ~
    @object
  end

  ####################
  #                  #
  # Instance Methods #
  #                  #
  ####################
  
  def tapp
    yield(self)
    ~self
  end

end

pointer_spec.rb

gem 'minitest'

require 'minitest/autorun'
require_relative 'pointer.shard.rb'

describe Pointer do

  describe :~ do

    it "defaults to nil" do
      (~Pointer.new).must_be_nil
    end

    it "can be assigned in the constructor" do
      (~Pointer.new(:foo)).must_equal :foo
    end

  end

  describe :<= do

    it "assigns the pointed value" do
      ptr = Pointer.new
      ptr <= :foo
      (~ptr).must_equal :foo
    end
  end

  describe :tapp do

    it "yields itself" do
      yielded = nil
      pointer = Pointer.new
      
      pointer.tapp do |ptr|
        yielded = ptr
      end

      yielded.must_equal pointer
    end

    it "returns the last assigned value" do
      Pointer.new.tapp do |ptr|
        ptr <= :foo
        ptr <= :bar
      end.must_equal :bar
    end

  end

end