Object Oriented Programming Advanced Usage – Arma Reforger

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This guideline requires the understanding of Object Oriented Programming Basics.

Casting

Casting is the act of "presenting" a value as another type. For example, if a class hierarchy is Animal > Dog > Cocker, a dog is an animal, a cocker is a dog (that is an animal), but a dog is not especially a cocker.

class Animal {} class Dog : Animal {} class Cocker : Dog {} class Labrador : Dog {}

Upcasting

Upcasting means seeing the class as one of its parents:

void Method() { Cocker cocker = new Cocker(); Animal animal = cocker; // OK, as a cocker is an animal string sentence = cocker; // error: cocker does -not- inherit from string };

Downcasting

Downcasting means seeing a parent class as a specific child - this must be done by manually casting:

void Method(Dog dog) { Cocker cocker1 = dog; // error: "Dog" is too generic to be casted as Cocker - it could be e.g a Labrador Cocker cocker2 = Cocker.Cast(dog); // OK: manual casting tells the code "the developer knows what he is doing" // if 'dog' is not castable as a Cocker, null is returned - the code does not crash Cocker cocker3; cocker3.Cast(dog); // alternative method }

Manual Casting

void Method() { float value1 = 4.9; int value2 = value1; // value2 = 4 as integer casting -truncates- the value, not rounds it string value3 = "result = " + (bool)value2; // "result = true", as a non-zero integer is true when casted to bool }

Template

A template is a class that allows a generic management for multiple types. Its methods cannot assume anything about the type.

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The generic type is by convention declared by the T letter.

// template class Item with generic type T class Item<Class T> { protected T m_data; void Item(T data) { m_data = data; } void SetData(T data) { m_data = data; } T GetData() { return m_data; } void PrintData() { Print(m_data); } };

void Method() { Item<string> stringItem = new Item<string>("Hello!"); // template class Item declared with type "string". In Item<string> class, all Ts are substituted with 'string' Item<int> intItem = new Item<int>(72); // template class Item declared with type "int". In Item<int> class, all Ts are substituted with 'int' stringItem.PrintData(); // prints "m_data = 'Hello!'" intItem.PrintData(); // prints "m_data = 72" }

Modding

A mod can inherit/replace an existing class with the use of the modded keyword.
It is used to inject inherited class into class hierarchy without modifying other scripts (especially suitable in modding). A modded class behaves like a class inherited from the original class (one can use super to access the original class). When a modded class is declared, the modded class will be instanced instead of the original class. Only classes within the same module can be modded (to mod a class in e.g GameLib module, the modded class has to be placed in the GameLib module).

// game class A { void Say() { Print("original Say method"); } }; // mod modded class A // this class automatically inherits from the original class A { void Say() { Print("modded Say method"); super.Say(); } }; void Test() { A a = new A(); // "modded class A" is instanced a.Say(); // prints 'modded Say method' then 'original Say method' }