Chapter 6 Flashcards
Variable scope examples
Local Var x =10
Global var $x = 10
Object(Instance) @x = 10, @side_length = side_length
Class Var @@x = 10
Classes:
A class is a collection of methods and data that are used as a blueprint to create multiple objects relating to that class.
Objects:
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.
Local variable:
A variable that can only be accessed and used from the current scope.
x = 10
Instance/object variable:
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
Global variable:
A variable that can be accessed and used from anywhere within the current program.
$x = 10
Class variable:
A variable that can be accessed and used within the scope of a class and all of its child objects
@@number_of_squares
Encapsulation:
The concept of allowing methods to have differing degrees of visibility outside of their class or associated object.
Polymorphism:
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).
Module:
An organizational element that collects together any number of classes, methods, and constants into a single namespace.
Namespace:
A named element of organization that keeps classes, methods, and constants from clashing.
Mix-in:
A module that can mix its methods in to a class to extend that class’s functionality.
Enumerable:
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.
Comparable:
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.
Class Method
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.
Super
looks up the inheritance chain and calls the method of the same name on the next highest class.
Private
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.
public
You could put private before one method, but then revert back to public methods again afterwards using public.
Protected
protected that makes a method private, but within the scope of a class rather than within a single object.
