Fake multiple inheritance example

modbuilder.rb

class ModBuilder
  def initialize path
    @path = path
    @files = []
  end

  def build! build_path
    puts "building #{self.class.name} in #{build_path}"
    build_mod_files!
    puts "Files: #{@files}"
    @files
  end

  def add_file name
    @files << name
  end
end

class FooMod < ModBuilder
  def build_mod_files!
    puts "build mod files for foo mod"
    add_file 'something'
  end
end

class BarMod < ModBuilder
  def build_mod_files!
    puts "build mod files for bar mod"
    add_file 'barthing'
  end
end

FooMod.new("game/path").build!("build/path")
BarMod.new("game/path").build!("barbuild/path")

class CompositeMod < ModBuilder
  def initialize *a
    @mods = klasses.map { |k| k.new *a }
  end

  def build_mod_files!
    ([self] + @mods).each_cons(2) do |last, mod|
      # note this will break stuff if mod does nontrivial init
      # and last clobbers its variables
      transfer_variables last, mod
      mod.build_mod_files!
    end
    transfer_variables @mods.last, self
  end

  def transfer_variables from, to
    from.instance_variables.each do |var|
      to.instance_variable_set var, from.instance_variable_get(var)
    end
  end
end

def CompositeMod *klasses
  Class.new(CompositeMod).tap do |klass|
    klass.send(:define_method, :klasses) { klasses }
  end
end

FooBarMod = CompositeMod(FooMod, BarMod)

class FooBarExtraMod < CompositeMod(FooMod, BarMod)
  def build_mod_files!
    super
    puts "extra handling for foo bar mod!"
  end
end

FooBarMod.new("game/path").build!("foobar/build/path")
FooBarExtraMod.new("game/path").build!("foobar/build/path")