Advanced Rails - Building Industrial-Strength Web Apps in Record Time

8 | Chapter 1: Foundational Techniques

The single-bordered box aroundobjrepresents a plain-old object instance. Note that
each box in this diagram is an object instance. However, the double-bordered boxes
represent objects that are instances of theClassclass (hence theirklasspointer
points to theClass object).

When we sendobj a message:

obj.to_s

this chain is followed:

1.obj’sklasspointer is followed toB;B’s methods (inm_tbl) are searched for a

matching method.

2. No methods are found inB.B’ssuperpointer is followed, andAis searched for
   methods.


3. No methods are found inA.A’ssuperpointer is followed, andObjectis searched
   for methods.


4. TheObjectclass contains ato_smethod in native code (rb_any_to_s). This is
   invoked, yielding a value like"#". Therb_any_to_smethod exam-
   ines the receiver’sklasspointer to determine what class name to display; there-
   fore,B is shown even though the method invoked resides inObject.

Including modules

Things get more complicated when we start mixing in modules. Ruby handles mod-
ule inclusion with ICLASSes,*which are proxies for modules. When you include a

Figure 1-3. Class instantiation

• ICLASS is Mauricio Fernández’s term for these proxy classes. They have no official name but are of type
  T_ICLASS in the Ruby source.

Object

A

super

B

super

obj klass