Simple rake extension to wrap a block with automatic loading and unloading of marshalled variables

marshal_wrap.rb

require 'rake/clean'

module MWsubs
  extend self

  def add_ext_sub(filename_in, ext_in)
    filename = filename_in.to_s
    # remove the period from the ext if it is there
    ext = (ext_in[/^\./]) ? ext_in[1..-1] : ext_in
    # add the extension unless it is alerady there
    (filename[/\.#{ext}$/]) ? filename : "#{filename}.#{ext}"
  end

  def add_ext(filename, ext)
    return nil if filename.nil?
    if filename.is_a? Array
      filename.map{|f| add_ext_sub(f, ext)}
    else
      add_ext_sub(filename, ext)
    end
  end

  def add_marshal(filename)
    add_ext(filename, '.marshal')
  end

  def marshal_save(object, filename)
    # will add '.marshal' to the end of the filename if it isn't already there
    File.open(add_marshal(filename), 'w') {|io| Marshal.dump(object, io)}
  end

  def marshal_load(filename)
    #will add '.marshal' to the filename if necessary
    File.open(add_marshal(filename)) {|io| Marshal.load(io)}
  end

  def load_inputs(filenames)
    [*filenames].map{|f| marshal_load(f)}
  end

  def save_outputs(objects_in, filenames_in)
    return if objects_in.nil?
    return if filenames_in.nil? || filenames_in.empty?
    filenames = [*filenames_in]
    objects = (filenames.count == 1) ? [objects_in] : objects_in
    Hash[objects.zip(filenames)].each {|o,f| marshal_save(o, f)}
  end

  def check_outputs(outputs, output_name_ar)
  
    n_expect = output_name_ar.count
    case n_expect
    when 0 # NP, the block might return an argument, but we don't need to save it
    when 1
      raise "Error: expecting an output from the block" if outputs.nil?
      # if we get an array of outputs they will just be mapped to a single marshal file
    else
      raise "Error: expecting #{n_expect} outputs from block but got none" if outputs.nil?
      n_received = outputs.count
      raise "Error: expecting #{n_expect} outputs from block but got #{n_received} instead" if n_expect != n_received
    end
  end

end

module Marshal_wrap
  extend self

  def marshal_wrap(*output_name_ar, &block)
    marsh_output_name_ar = MWsubs.add_marshal(output_name_ar)
    # rake file tasks can only accept one file as a target
    target_file = marsh_output_name_ar[0]
    params = block.parameters.map{|p| p[1]}
    file target_file => MWsubs.add_marshal(params)
    file target_file do |f|
      puts "Making #{f.name}"
      inputs = MWsubs.load_inputs(params)
      outputs = block.(inputs)
      MWsubs.check_outputs(outputs, output_name_ar)
      MWsubs.save_outputs(outputs, output_name_ar)
    end
    task default: target_file
    CLOBBER.include(marsh_output_name_ar)
  end

end