Programming Ruby: The Pragmatic Programmers' Guide (Second Edition): Internal Architecture: klass and super Pointers

At the C-level, Ruby objects are represented by structures that separate data from behavior through a pointer-based hierarchy. The klass pointer connects an instance to its "associated class" (where methods live), while the super pointer connects classes to their ancestors, creating a structural map that the Ruby VM uses to resolve inheritance.

1. The klass Pointer & Flags

Every Ruby object contains a header with a klass pointer and a bitmask of flags. These flags identify the object's internal state, such as marking automatically created "virtual classes" with a 'V' to handle singleton method assignments.

2. Decoupling State (Figure 24.1)

An instance like lucille stores its own unique instance variables, but it possesses no methods of its own. Its klass pointer directs the VM to the Guitar class object's method table.

3. The Inheritance Chain

When lucille.play() is called, Ruby follows the klass pointer. If the method isn't found in Guitar, it follows the super pointer to Object, granting access to clone or dup.

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QUESTION 1

Where are an object's methods (like def play()) actually stored?

Inside the instance structure itself alongside variables.

In the method table of the class pointed to by 'klass'.

In a global Ruby registry.

Inside the 'super' pointer destination only.

QUESTION 2

What does the 'V' flag represent in a class's internal flags?

Version: The Ruby version used to create it.

Virtual: It is an automatically created singleton class.

Value: The class represents a primitive type.

Validated: The class has passed security checks.

QUESTION 3

What is the primary function of the super pointer in a class object?

To point to the object's instance variables.

To point to the class's own class (metaclass).

To point to the parent class for method lookup.

To link an instance back to its constructor.

QUESTION 4

If you define def Guitar.strings, where is that method stored?

In the Guitar class method table.

In a virtual class inserted into Guitar's own hierarchy.

In the Object class table.

Directly inside the 'lucille' instance.

QUESTION 5

Does calling lucille.clone use the klass or super pointer first?

It follows klass to Guitar, then super to Object.

It bypasses klass and goes straight to Object.

It searches the local iv_tbl first.

It follows super from the instance.