Arrayはすげ替えつつFiddle::Pointerは使い回すクラス・PackedData

packed_data.rb

# -*- coding: utf-8 -*-
require 'fiddle'

# Array -> Fiddle::Pointer conversion
class PackedData
  attr_reader :data, :pointer

  def initialize( src )
    @source = src   # Array or String built from packed Array
    @data = nil     # String
    @pointer = nil  # Fiddle::Pointer
  end

  def set_source( src )
    if @source.is_a?(Array) || @source.is_a?(String)
      @source = src
    else
      raise ArgumentError
    end
    @data = nil
  end

  def build( template_string = nil )
    # Prepare data
    if @source.is_a?(Array)
      raise ArgumentError if template_string == nil
      @data = @source.pack( template_string )
    elsif @source.is_a?(String)
      @data = @source
    else
      raise RuntimeError
    end

    # Build pointer
    if @pointer == nil || @pointer.size < @data.size
      @pointer = Fiddle::Pointer[@data]
    else
      @pointer[0, @data.size] = @data
    end
  end

  def to_ptr
    return @pointer
  end

  def release
    @source = nil
    @data = nil
    @pointer = nil
  end
end