#instance_eval does not change the current namespace

instance_eval_module_nesting.rb

module Foo
  class Bar
    BAZ = 'Hello'

    def print_module_nesting
      p Module.nesting
    end
  end
end

bar_instance = Foo::Bar.new

puts ' Normal '.center(30, '=')
bar_instance.print_module_nesting

puts
puts ' #instance_eval '.center(30, '=')
bar_instance.instance_eval do
  print_module_nesting
  p Module.nesting
  p Foo::Bar::BAZ
  p BAZ
end

result.txt

$ ruby --version
ruby 2.1.2p95 (2014-05-08 revision 45877) [x86_64-darwin13.0]
$ ruby instance_eval_module_nesting.rb
=========== Normal ===========
[Foo::Bar, Foo]

======= #instance_eval =======
[Foo::Bar, Foo]
[]
"Hello"
instance_eval_module_nesting.rb:22:in `block in <main>': uninitialized constant BAZ (NameError)
        from instance_eval_module_nesting.rb:18:in `instance_eval'
        from instance_eval_module_nesting.rb:18:in `<main>'