I Spoke at RubyConfIndia 2016 about Closer look at method scopes in ruby. In this talk I did code walk through of MRI implementation of ruby(ruby 2.2). And important data structure "rb_control_frame_t". http://rubyconfindia.org/

1. Ruby is Awesome!

2. –Sumit Mahamuni
@meetmahamuni
https://github.com/sumitmah

3. Some Background
about the talk

4. class Foo
def public_method
puts "I'm Public"
end
protected
def protected_method
puts "I'm protected"
end
private
def private_method
puts "I'm private"
end
end

5. > foo = Foo.new
> foo.public_method
#=> I'm Public

6. > foo.protected_method
> NoMethodError: protected method `protected_method'
called for #<Foo>

7. > foo.private_method
#=>NoMethodError: private method `private_method'
called for #<Foo>

8. class Bar < Foo
end
> bar = Bar.new
> bar.public_method
#=> I'm Public
> bar.protected_method
#=> NoMethodError: protected method `protected_method'
called for #<Foo>
> bar.private_method
#=>NoMethodError: private method `private_method' called for
#<Foo>

9. class Foo
private
def private_method
puts "I'm private"
end
def self.private_method
puts "I'm private"
end
end

10. > foo = Foo.new
> foo.private_method
#=> NoMethodError: private method `private_method' called for
#<Foo>

11. > Foo.private_method
#=> I'm private

12. foo
m_table
Foo
instance_private_method
#<Class:Foo>
m_table
class_private_method
class Foo
private
def instance_private_method
puts "I'm private"
end
def self.class_private_method
puts "I'm private"
end
end

13. What is “private”?

14. /* vm_method.c */
void
Init_eval_method(void)
{
...
rb_define_private_method(rb_cModule, “private",
rb_mod_private, -1);
...
}

15. /* class.c */
static VALUE
boot_defclass(const char *name, VALUE super);
void
Init_class_hierarchy(void)
{
rb_cBasicObject = boot_defclass("BasicObject", 0);
rb_cObject = boot_defclass("Object", rb_cBasicObject);
rb_cModule = boot_defclass("Module", rb_cObject);
rb_cClass = boot_defclass("Class", rb_cModule);
…
}

16. Object structure
> class A
> end
=> nil
> A.class
=> Class
> A.class.ancestors
=> [Class, Module, Object, Kernel, BasicObject]

17. class WhatIsPrivate
private
end

18. /* vm_method.c */
static void
vm_cref_set_visibility(rb_method_visibility_t method_visi, int
module_func)
{
rb_scope_visibility_t *scope_visi =
(rb_scope_visibility_t*)&rb_vm_cref()->scope_visi;
scope_visi->method_visi = method_visi;
scope_visi->module_func = module_func;
}

19. /* vm.c */
rb_cref_t *
rb_vm_cref(void)
{
rb_thread_t *th = GET_THREAD();
rb_control_frame_t *cfp =
rb_vm_get_ruby_level_next_cfp(th, th->cfp);
if (cfp == NULL) {
return NULL;
}
return rb_vm_get_cref(cfp->ep);
}

20. This image is taken from Ruby under microscope book.

21. This image is taken from Ruby under microscope book.

22. class WhatIsDefineMethod
private
def i_am_private
end
def self.method_defined_on_self_object
end
end

23. static void
vm_define_method(rb_thread_t *th, VALUE obj, ID id, VALUE iseqval,
int is_singleton);

24. /* vm.c */
static void
vm_define_method(rb_thread_t *th, VALUE obj, ID id,
VALUE iseqval, int is_singleton)
{
VALUE klass;
rb_method_visibility_t visi;
rb_cref_t *cref = rb_vm_cref();
if (!is_singleton) {
klass = CREF_CLASS(cref);
visi = rb_scope_visibility_get();
}
else { /* singleton */
/* class and frozen checked in this API */
klass = rb_singleton_class(obj);
visi = METHOD_VISI_PUBLIC;
}
…
}

25. static rb_method_visibility_t
rb_scope_visibility_get(void)
{
rb_thread_t *th = GET_THREAD();
rb_control_frame_t *cfp =
rb_vm_get_ruby_level_next_cfp(th, th->cfp);
if (!vm_env_cref_by_cref(cfp->ep)) {
return METHOD_VISI_PUBLIC;
}
else {
return CREF_SCOPE_VISI(rb_vm_cref())->method_visi;
}
}

26. object
class WhatIsDefineMethod
private
def i_am_private
end
def self.method_defined_on_self_object
end
end
m_table
WhatIsDefineMethod
i_am_private
#<Class:WhatIsDefineMethod>
m_table
method_defined_on_self_object

27. class AnyClass
class << self
def any_public_method
end
protected
def any_protected_method
end
private
def any_private_method
end
end
end
CFP
[AnyClass]
CFP
CFP
CFP
[self]
Ruby call stack

28. –Sumit Mahamuni
@meetmahamuni
https://github.com/sumitmah
“Thanks.”