Chapter 6

Question 1

Variable scope examples

Answer 1

Local Var x =10
Global var $x = 10
Object(Instance) @x = 10, @side_length = side_length
Class Var @@x = 10

Question 2

Classes:

Answer 2

A class is a collection of methods and data that are used as a blueprint to create multiple objects relating to that class.

Question 3

Objects:

Answer 3

An object is a single instance of a class.

An object of class Person is a single person. An object of class Dog is a single dog. If you think of objects as real-life objects, a class is the classification, whereas an object is the actual object or “thing” itself.

Question 4

Local variable:

Answer 4

A variable that can only be accessed and used from the current scope.

x = 10

Question 5

Instance/object variable:

Answer 5

A variable that can be accessed and used from the scope of a single object. An object’s methods can all access that object’s object variables.

@side_length = side_length

Question 6

Global variable:

Answer 6

A variable that can be accessed and used from anywhere within the current program.

$x = 10

Question 7

Class variable:

Answer 7

A variable that can be accessed and used within the scope of a class and all of its child objects

@@number_of_squares

Question 8

Encapsulation:

Answer 8

The concept of allowing methods to have differing degrees of visibility outside of their class or associated object.

Question 9

Polymorphism:

Answer 9

The concept of methods being able to deal with different classes of data and offering a more generic implementation (as with the area and perimeter methods offered by your Square and Triangle classes).

Question 10

Module:

Answer 10

An organizational element that collects together any number of classes, methods, and constants into a single namespace.

Question 11

Namespace:

Answer 11

A named element of organization that keeps classes, methods, and constants from clashing.

Question 12

Mix-in:

Answer 12

A module that can mix its methods in to a class to extend that class’s functionality.

Question 13

Enumerable:

Answer 13

A mix-in module, provided as standard with Ruby, that implements iterators and list-related methods for other classes, such as collect, map, min, and max. Ruby uses this module by default with the Array and Hash classes.

Question 14

Comparable:

Answer 14

A mix-in module, provided as standard with Ruby, that implements comparison operators (such as <, >, and ==) on classes that implement the generic comparison operator <=>.

To provide these methods, the Comparable module uses the <=> comparison operator on the class that includes it. <=> returns −1 if the supplied parameter is higher than the object’s value, 0 if they are equal, or 1 if the object’s value is higher than the parameter.

Question 15

Class Method

Answer 15

class method is denoted with self., where self represents the current class, so def self.test_method defines the method as being specific to the class.

Question 16

Super

Answer 16

looks up the inheritance chain and calls the method of the same name on the next highest class.

Question 17

Private

Answer 17

private tells Ruby that any methods declared in this class from there on should be kept private.

This means that only code within the object’s methods can access those private methods, whereas code outside of the class cannot.

Question 18

public

Answer 18

You could put private before one method, but then revert back to public methods again afterwards using public.

Question 19

Protected

Answer 19

protected that makes a method private, but within the scope of a class rather than within a single object.