FFI internals 6

ffi6.rb

require 'ffi'

module RubyInternals
  extend FFI::Library
  ffi_lib(FFI::CURRENT_PROCESS)

  attach_variable :ptr_vm_core, :rb_mRubyVMFrozenCore, :pointer

  attach_function :const_def_pointer, :rb_define_const,
    [:pointer, :string, :pointer], :void

  attach_variable :ptr_object_class, :rb_cObject, :pointer
  const_def_pointer(ptr_object_class, "RubyCore", ptr_vm_core)

  def define_iseq_singleton_method(mod,sel,iseq)
    mod.module_eval do
      RubyCore.send("core#define_singleton_method",mod,sel,iseq)
    end
  end

end

module Greeter
  extend RubyInternals

  iseq = RubyVM::InstructionSequence.compile <<-RUBY
    puts "Hello, world."
  RUBY

  define_iseq_singleton_method(self,:greet,iseq)
end

Greeter.greet