Extract Method in Ruby

Refactoring Name: Extract Method

Original Code (taken from the checkr project):

  def process_args(exp)
    @saw_asgn = true
    args = []
    exp.length.times do
      element = exp.shift
      if element.kind_of? Array
        args << process(element)
      else
        args << init_var(element)
      end
    end
    s(:args,
      *args)
  end


  def process_block(exp)
    unless exp[1] != [:nil]
      @errors << "no-op in block"
    end
    args = []
    exp.length.times do
      element = exp.shift
      if element.kind_of? Array
        args << process(element)
      else
        args << init_var(element)
      end
    end
    s(:block,
      *args)
  end

Explanation and mechanics:
process_block was written by creating the new functionality (the unless block at the beginning) and copying the args building code from process_args. This created a block of duplicate code that I didn't want to maintain, so I extracted a method like this:

• I created a new method, build_sexp
• I moved the code from process_block into it
• I replaced the code in process_block with a call to build_sexp
• I reran my test suite to verify that nothing broke[1]
• I replaced the original code in process_args with a call to build_sexp
• I reran my test suite to verify that nothing broke

New Code (ordered by method name):

  def build_sexp(exp)
    args = []
    exp.length.times do
      element = exp.shift
      if element.kind_of? Array
        args << process(element)
      else
        args << init_var(element)
      end
    end
    args
  end

  def process_args(exp)
    @saw_asgn = true
    args = build_sexp(exp)
    s(:args,
      *args)
  end

  def process_block(exp)
    unless exp[1] != [:nil]
      @errors << "no-op in block"
    end

    args = build_sexp(exp)
    s(:block,
      *args)
  end

This actually lead to a couple of other refactorings. We didn't like the fact that build_sexp did two things (emptied the original array, and processed each member of the new array), so we extracted another method. Then we realized that our two new methods were poorly named, so we performed Rename Method on both of them. we're not sure we'll use the code we ended up with, as it still hides some functionality that we might want to keep explicit, but it was a good exercise to go through.