Difference between revisions of "Intermediate C++ Game Programming Tutorial 17"
From Chilipedia
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[https://youtu.be/21uaUOeOof8 Tutorial 17.2] | [https://youtu.be/21uaUOeOof8 Tutorial 17.2] | ||
| + | <div class="mw-collapsible mw-collapsed"><br /> | ||
* Revisiting the "is-a" principle of Inheritance. Applying it to build a class hierarchy [https://youtu.be/21uaUOeOof8?t=51 0:51] | * Revisiting the "is-a" principle of Inheritance. Applying it to build a class hierarchy [https://youtu.be/21uaUOeOof8?t=51 0:51] | ||
* Abstract vs. Concrete classes [https://youtu.be/21uaUOeOof8?t=3m20s 3:20] | * Abstract vs. Concrete classes [https://youtu.be/21uaUOeOof8?t=3m20s 3:20] | ||
| + | <div class="mw-collapsible-content"> | ||
** Abstract (parent) classes are not supposed to be instantiated (constructors are protected) | ** Abstract (parent) classes are not supposed to be instantiated (constructors are protected) | ||
** Concrete (child) classes are supposed to be instantiated | ** Concrete (child) classes are supposed to be instantiated | ||
| + | </div> | ||
* Application of abtract classes on multiple levels [https://youtu.be/21uaUOeOof8?t=4m09s 4:09] | * Application of abtract classes on multiple levels [https://youtu.be/21uaUOeOof8?t=4m09s 4:09] | ||
* Building the Meme Fighter class hierarchy (Abstract class) [https://youtu.be/21uaUOeOof8?t=5m28s 5:28] | * Building the Meme Fighter class hierarchy (Abstract class) [https://youtu.be/21uaUOeOof8?t=5m28s 5:28] | ||
| + | <div class="mw-collapsible-content"> | ||
** Introducing the modifier <code>mutable</code> (an access specifier for data members) [https://youtu.be/21uaUOeOof8?t=10m06s 10:06] | ** Introducing the modifier <code>mutable</code> (an access specifier for data members) [https://youtu.be/21uaUOeOof8?t=10m06s 10:06] | ||
** When writing a <code>const</code> member function (i.e. a member function that does not change data members in the class), a <code>mutable</code> data member may be changed in that function | ** When writing a <code>const</code> member function (i.e. a member function that does not change data members in the class), a <code>mutable</code> data member may be changed in that function | ||
| + | </div> | ||
* Building the Meme Fighter class hierarchy (Concrete classes) [https://youtu.be/21uaUOeOof8?t=13m03s 13:03] | * Building the Meme Fighter class hierarchy (Concrete classes) [https://youtu.be/21uaUOeOof8?t=13m03s 13:03] | ||
* Giving the implemented code a test run [https://youtu.be/21uaUOeOof8?t=16m49s 16:49] | * Giving the implemented code a test run [https://youtu.be/21uaUOeOof8?t=16m49s 16:49] | ||
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* Getting a class diagram in Visual Studio [https://youtu.be/21uaUOeOof8?t=19m26s 19:26] | * Getting a class diagram in Visual Studio [https://youtu.be/21uaUOeOof8?t=19m26s 19:26] | ||
* Closing two points of advice [https://youtu.be/21uaUOeOof8?t=19m55s 19:55] | * Closing two points of advice [https://youtu.be/21uaUOeOof8?t=19m55s 19:55] | ||
| + | <div class="mw-collapsible-content"> | ||
** Never break the "is-a" rule | ** Never break the "is-a" rule | ||
** Don't go crazy with applying inheritance | ** Don't go crazy with applying inheritance | ||
| + | </div> | ||
| + | </div> | ||
== Part 2 Class Specification == | == Part 2 Class Specification == | ||
Latest revision as of 22:46, 13 October 2019
This two-part lesson teaches the basics of inheritance, how it works and what motivates its use, with ample concrete coding examples. Also taught here is the keyword mutable, for some reason.
Contents
Topics Covered
Part 1
- How to inherit from a class
- Referencing a child type with a parent reference/ptr
- Inheritance and constructors
- Overriding parent functions
- Invoking overridden versions of functions
- Access specifier
protected
Part 2
- Hierarchical inheritance
- Abstract vs. concrete classes
-
mutabledata members
Video Timestamp Index
- What is inheritance? Introducing a simple example
class ChildClass : public ParentClass {...};0:15 - Different language used for the same concept 1:45:
- to "inherit" a class, from "parent" to "child",
- to "extend" a class, from "base" to "extended",
- to "derive" a class, from "base" to "derived",
- to "sub-class" a class, from "superclass" to "subclass" (used in Java)
- Why is inheritance important? no clutter, no repetition of code, no tampering inside deployed classes 2:44
- Fictitious but instructive
SmasherandEliteSmasherclass example 5:08 - Inheritance creates an "Is-a relationship" 8:15
- A child class "is-a [kind of]" parent class, so you can pass a child object to functions that expect a reference to a parent object
- The ability to refer to a child type with a parent reference (or pointer), allows us to create functions that can work over many types, as long as they all inherit from a common parent
- Inheritance and constructors: you can't inherit (default) constructors 9:49
- The base class of a class behaves like the first data member of the extended class: it is initialized (constructed) first
- The default constructor of a child class has to call a constructor of the parent class
- Overriding parent functions in the child class 13:22
- In addition to extending functionality of a parent class in a child class, overriding allows you to alter functionality, if you have to
- You can invoke the parent version of an overridden function by prefixing the parent class name
ParentClass::OverriddenParentFunction(); - The private members of the parent class are not accessible to the child class
- Introducting the
protected:access specifier in classes 16:34
- Form of access control that enables children to access members (while keeping members private to all other scopes)
- Allows you to apply proper encapsulation of the parent class by setting a separate protected interface only for its children
- ROI "Return on invested time" should guide your choice to either i) protect your members, ii) keep your members private but build a proteced interface
- Revisiting the "is-a" principle of Inheritance. Applying it to build a class hierarchy 0:51
- Abstract vs. Concrete classes 3:20
- Abstract (parent) classes are not supposed to be instantiated (constructors are protected)
- Concrete (child) classes are supposed to be instantiated
- Application of abtract classes on multiple levels 4:09
- Building the Meme Fighter class hierarchy (Abstract class) 5:28
- Introducing the modifier
mutable(an access specifier for data members) 10:06 - When writing a
constmember function (i.e. a member function that does not change data members in the class), amutabledata member may be changed in that function
- Introducing the modifier
- Building the Meme Fighter class hierarchy (Concrete classes) 13:03
- Giving the implemented code a test run 16:49
- Recap of topics covered 18:40
- Getting a class diagram in Visual Studio 19:26
- Closing two points of advice 19:55
- Never break the "is-a" rule
- Don't go crazy with applying inheritance
Part 2 Class Specification
All of the MemeFighter entities of the system will have the following shared functionality:
- Member data for
name(string),hp,speed, andpower(int) - Getters for name, initiative (speed + 2d6), and alive state
-
Punchfunction that takes a different entity and applies damage (power + 2d6) to it -
Tickfunction where the entity recovers 1d6 hp
Functions should narrate actions / effects when it makes sense. Tests should be made to check whether an entity is alive before an action is performed (dead characters can't punch, recover, etc.)
There are two concrete MemeFighter entites: MemeFrog and MemeStoner
MemeFrog:
- Has 69 hp, 7 speed, and 14 power
- Has a
SpecialMovefunction that takes an entity and has a 1/3 chance of dealing 3d6 + 20 damage - Takes 1d6 of damage every turn
MemeStoner:
- Has 80 hp, 4 speed, and 10 power
- Has a
SpecialMovefunction that takes no parameters and has a 1/2 chance of adding 3 speed, increasing power by 69/42, adding 10 hp, and adding "Super" to the entity's name
Source Code
Links
C++ FAQ on protected
Stack Overflow question about inheritance
