Renaming an anonymous class in Ruby...

gistfile1.txt

kj@kj-thinkpad ~ % cat rename.rb
#!/usr/bin/env ruby

require 'fiddle'

libruby = Fiddle::Handle.new
rb_set_class_path_string = Fiddle::Function.new(
  libruby['rb_set_class_path_string'],
  [
    Fiddle::TYPE_UINTPTR_T,
    Fiddle::TYPE_UINTPTR_T,
    Fiddle::TYPE_UINTPTR_T
  ],
  Fiddle::TYPE_VOID
)

GC.disable
def object_addr(o)
  istr = Object.instance_method(:inspect).bind(o).call
  istr =~ /:(0x[0-9A-Fa-f]+)>/
  $1.to_i(16)
end

cl = Class.new
puts "class => #{cl}"

name = "Foo::BarKlass"
rb_set_class_path_string.call(object_addr(cl), object_addr(Object), object_addr(name))
puts "class => #{cl}"

kj@kj-thinkpad ~ % /opt/ruby33/bin/ruby rename.rb
class => #<Class:0x00007f1e3fcd1360>
class => Foo::BarKlass