`def` in block argument of Struct.new defines a top-level procedure

[tsahara]

Customer = Struct.new(:name, :address) do
  p self
  def greeting
    "Hello!"
  end
end

dave = Customer.new("Dave", "123 Main")
p dave.name     #=> "Dave"
p dave.greeting #=> "Hello Dave!"
p greeting      #=> expected to raise NameError

On CRuby, the last line raises a NameError exception because the method greeting is not defined on top-level (but an accessor of Customer). It is an expected behavior.

#<Class:0x00157a1b98f990>
"Dave"
"Hello!"
a.rb:11:in `<main>': undefined local variable or method `greeting' for main:Object (NameError)

On mruby, it shows "Hello!" and self in the block is not an instance of Customer but main(!):

main
"Dave"
"Hello!"
"Hello!"