ブロック中の数値が全て2倍になるメソッド書いてみた

double.rb

#! ./ruby -I.ext/x86_64-darwin14 --disable-gems
require '-test-/iseq_load/iseq_load'

def double(&block)
  iseq_data_magic_index         = 0
  iseq_data_major_version_index = 1
  iseq_data_minor_version_index = 2
  iseq_data_format_type_index   = 3
  iseq_data_misc_index          = 4
  iseq_data_label_index         = 5
  iseq_data_path_index          = 6
  iseq_data_absolute_path_index = 7
  iseq_data_first_lineno_index  = 8
  iseq_data_type_index          = 9
  iseq_data_locals_index        = 10
  iseq_data_params_index        = 11
  iseq_data_catch_table_index   = 12
  iseq_data_bytecode_index      = 13

  iseq = RubyVM::InstructionSequence.of(block)

  iseq_data    = iseq.to_a
  new_bytecodes = []
  old_bytecodes = iseq_data[iseq_data_bytecode_index]
  old_bytecodes.each do |bytecode|
    if bytecode.kind_of?(Array) && bytecode.first == :putobject && bytecode.last.kind_of?(Fixnum)
      new_bytecodes << [bytecode.first, bytecode.last * 2]
    else
      new_bytecodes << bytecode
    end
  end

  new_iseq_data = iseq_data.dup
  new_iseq_data[iseq_data_bytecode_index] = new_bytecodes

  # topじゃないとevalときエラーになるのでblockをtopに細工
  if new_iseq_data[iseq_data_type_index] == :block
    new_iseq_data[iseq_data_type_index] = :top
  end

  new_iseq = RubyVM::InstructionSequence.iseq_load(new_iseq_data)
  new_iseq.eval
end

double { puts 3 * 5 }
# 60