Object Oriented Programming

Classes

A class is an expanded concept of a data structure: instead of holding only data, it can hold both data and functions.

An object is an instantiation of a class. In terms of variables, a class would be the type, and an object would be the variable.

Classes are generally declared using the keyword class, with the following format:

Source code (UnigineScript)

class class_name {
	access_specifier_1: 
	member1;
	access_specifier_2:
	member2; 
	// ... 
} object_names;
	
// class_name - valid identifier for the class
// object_names - an optional list of names for objects of this class

The body of the declaration can contain members, that can be either data or function declarations, and optionally access specifiers.

NoticeThere is no protected access level modifier, there are only public and private ones. All class members are public by default.

UnigineScript Class Types

There are 3 types of classes applicable in UnigineScript:

Engine Classes
User-Defined Classes
External Classes (exported from the C++ by a script)

Engine Classes

You can see the list of available Engine Classes here.

User-Defined Classes

User-Defined Classes are classes defined by user. Inheritance is supported.

Source code (UnigineScript)

/* user-defined class
 */
class Foo {
	// member variables
	int a;
	int b;
	// constructor
	Foo(int a,int b) {
		this.a = a;
		this.b = b;
	}
	// destructor
	~Foo() {}
	// member function (method)
	void print() {
		log.message("a is %d, b is %d\n",a,b);
	}
};

// create a new instance of the Foo class
Foo foo = new Foo(10,20);
// call a method of that instance
foo.print(); // Output: a is 10, b is 20
// force object destruction
delete foo;

Note that you always manipulate with references to objects but not with the objects themselves. That is why when you assign one object to another, it means that you simply copy the reference. Once the object is destroyed, its references aren't functional anymore.

Source code (UnigineScript)

Foo f0 = new Foo();
Foo f1 = f0;
f1.print();
delete f0;
f1.print(); // run-time error: the object is null

Methods are set up at the compile-time, therefore:

Source code (UnigineScript)

Foo foo = new Foo();
foo.print(); // ok
foo = 10;
foo.print(); // run-time error
int i = new Foo();
i.print(); // compile-time error

External Classes

External classes are classes exported from C++. You can read how to export a class from C++ here.

Access Specifiers

Access pecifiers modify the access rights that the members following them acquire. UnigineScript provides two different specifiers for accessing class members:

public means that a member can be accessed from the outside of the class instance.
private means that such member is accessible from within other members of the same class and members of the inherited classes.

Notice

All class members are public by default.

Source code (UnigineScript)

class Foo {
	int public_i;
	void public_foo() { log.message("Public (no access specifier)\n"); }		
	private:
		int private_i;
        void private_foo() { log.message("Private\n"); }		
	public:
        int public_j;
        void public_bar() { log.message("Public\n"); }	
};

For example, in case if a class is inherited from Foo:

Source code (UnigineScript)

class Bazz : Foo {
	void foo() {
		Foo::public_foo();
		Foo::private_foo();
	}
};
	
Bazz b = new Bazz();
b.foo();

The result will be:

Output

Public (no access specifier)
Private

Constructors and Destructors

Constructors and new

For a class to be used, it should be instantiated. This is done using constructors. A constructor creates an instance of a class and returns it. Here is how a constructor can be defined:

Source code (UnigineScript)

class Foo {
	// member variable
	int a;
	// constructor
	Foo(int a) {
		// do something here
	}
// other functions
	
};

The constructor is a method that:

Has the same name as the class to which it belongs.
Does not have a return type specifier in its declaration and does not use the return or yield statement.

If the constructor is defined outside the class declaration, it should be done like this:

Source code (UnigineScript)

class Foo {
	// constructor declaration
	Foo();
	// other stuff
	…
};
	
// constructor definition
void Foo::__Foo__() {
	// do something here
}

To invoke a constructor, use the new operator as follows:

Source code (UnigineScript)

Foo fooInstance = new Foo(5);

Also the new operator can receive a string:

Source code (UnigineScript)

Foo fooInstance = new("Foo",5);

Destructors and delete

If a class instance is no longer needed and it's time for it to pass away, it should be properly freed. That is why a destructor is called before the occupied memory is marked as free. Here is how a destructor can be defined:

Source code (UnigineScript)

class Foo {
	// member variable
	int a;
	// destructor
	~Foo() {
		// do something here
	}
	// other functions
	…
};

The destructor is a method, which:

Has the same name as the class to which it belongs.
Has a prefix ~ before its name.
Does not have a return type specifier in its declaration and does not use the return or yield statement.

If the destructor is defined outside the class declaration, it should be done like this:

Source code (UnigineScript)

class Foo {
	// destructor declaration
	~Foo();
	// other stuff
	…
};

// destructor definition
void Foo::__~Foo__() {
// do something here
…
}

To invoke a destructor explicitly, you need to write something like this:

Source code (UnigineScript)

delete fooInstance;

Overloading

Overloading allows functions and operators to have the same name but with different parameters.

Function Overloading

UnigineScript allows Function Overloading.

Source code (UnigineScript)

int foo(int a,int b) {
	return a * b;
}

int foo(int a,int b,int c) {
	return a + b + c;
}

log.message("%d\n",foo(2,3)); // the result is: 2*3=6
log.message("%d\n",foo(2,3,4)); // the result is: 2+3+4=9

Operator Overloading

Operator overloading allows operators to have different implementations depending on their arguments. You can provide your own operator to a class by overloading the built-in operator to perform some specific computation when the operator is used on objects of that class.

The name of an overloaded operator is operator x, where x is the operator, available for overloading in UnigineScript:

operator+
operator-
operator*
operator/
operator%
operator<
operator>
operator==
operator<=
operator>=
operator!=
__set__ (for [])
__get__ (for [])

The following example represents overloading of the operator+, operator- and operator* for the class Vec3:

Source code (UnigineScript)

class Vec3 {
	
	float x,y,z;
	
	Vec3(float x,float y,float z) {
		this.x = x; this.y = y; this.z = z;
	}
	
	Vec3 operator+(Vec3 v0,Vec3 v1) {
		return new Vec3(v0.x + v1.x,v0.y + v1.y,v0.z + v1.z);
	}
	
	Vec3 operator-(Vec3 v0,Vec3 v1) {
		return new Vec3(v0.x - v1.x,v0.y - v1.y,v0.z - v1.z);
	}
	
	Vec3 operator*(Vec3 v,float f) {
		return new Vec3(v.x * f,v.y * f,v.z * f);
	}
};

Vec3 v0 = new Vec3(1,2,3);
Vec3 v1 = new Vec3(4,5,6);

Vec3 res = (v0 + v1) * 13.13 + (v1 - v0) * 31.31 + v0 * 0.5;
log.message("%f %f %f\n",res.x,res.y,res.z);

// the result is: 160.080002 186.839996 213.600006

The example of operator< overloading:

Source code (UnigineScript)

class Class {
	string name;
	Class(string name) {
		this.name = name;
	}
	int operator<(Class c0,Class c1) {
		return (c0.name < c1.name);
	}
};

Class classes[0];
forloop(int i = 0; 8) {
	classes.append(new Class(string(rand(0,100))));
}

classes.sort();
foreach(Class c; classes) {
	log.message("%s ",c.name);
}
log.message("\n");

// the result is: 15 35 77 83 86 86 92 93

Overload operator[] in user-defined class:

Source code (UnigineScript)

class Foo {
    mat4 m;
    void __set__(Foo f,int index,int value) {
        f.m[index] = value;
    }
    int __get__(Foo f,int index) {
        return f.m[index];
    }
};

Foo f = new Foo();
f[0] = 10;
f[1] = f[0];
log.message("%g %g\n",f[0],f[1]);

// the result is: 10 10

Keywords

this Keyword

Sometimes it is important to reference the object, for which a method is invoked. In such a situation, this keyword is helpful; it is reference to an object itself, available for member functions of the class.

Source code (UnigineScript)

class Foo {
	int a;
	int b;
	// usage in a constructor
	Foo(int a,int b) {
		this.a = a;
		this.b = b;
	}
	// usage in a method
	void print() {
		log.message("a is %d, b is %d, object is %s\n",a,b,typeinfo(this));
	}
};

Foo foo = new Foo(10,20);
foo.print();

Output

a is 10, b is 20, object is Foo (0:0)

Here 0:0 means "class ID is 0, object ID is 0"

super Keyword

Base class functions can be overridden in the derived class. However, you can call such functions from the derived class by using the super keyword. For example, the foo() function is overriden in the Bar class, so, the foo() function of the Foo class can be called using super.

Source code (UnigineScript)

class Foo {
  void foo() { log.message("base\n"); }
};
class Bar : Foo{
  void foo() { log.message("derived\n"); }
  void bar() {
    super.foo();   // prints "base"
    this.foo();    // prints "derived"
  }
};
Bar bar = new Bar();
bar.bar();

The result will be:

Output

base
derived

Inheritance

In UnigineScript, derived classes can inherit all public methods and data members from one or multiple base classes.

There is a peculiarity of the class inheritance in UnigineScript:

When a user class is inherited from another class, both automatically support virtual methods.
Notice
You can declare the virtual function by using the virtual keyword, but it's optional.

Source code (UnigineScript)

class Foo {
	int f = -13;
	int array[2] = ( 0, 1 );
	
	Foo(int i) { f = i; }
	void foo() { log.message("Foo::foo %d: %d %d\n",f,array[0],array[1]); }
};

class Bar : Foo {
	// f is initialized in the base class
	int b = 2;
	int array[2] = ( 2, 3 );
	
	Bar(int i) { b = i; }
	void bar() { log.message("Bar::bar %d %d: %d %d\n",f,b,array[0],array[1]); }
	void foo() { log.message("Bar::foo %d %d: %d %d\n",f,b,array[0],array[1]); }
};

class Bazz : Bar {
	// f is initialized in the base class
	int b = -23;
	int array[2] = ( 4, 5 );
	
	Bazz(int i) { b = i; }
	void foo() { log.message("Bazz::foo %d %d: %d %d\n",f,b,array[0],array[1]); }
};

Foo f = new Foo(13);
Bar b = new Bar(133);
Bazz bz = new Bazz(1333);

void foo(Foo f) {
	f.foo();
	f.call("foo");
}

foo(f);
foo(b);
foo(bz);

The result will be:

Output

Foo::foo 13: 0 1
Foo::foo 13: 0 1
Bar::foo -13 133: 2 3
Bar::foo -13 133: 2 3
Bazz::foo -13 1333: 4 5
Bazz::foo -13 1333: 4 5

Calling the Base Class Constructor

It is also possible to call the base class constructor in the inherited class.

Source code (UnigineScript)

class Foo {
        Foo(int a,int b) { log.message("Foo::Foo(): %d %d\n",a,b); }
};

class Bar : Foo {
        Bar(int a,int b) : Foo(a + 3,b + 5) { }
};

Bar b = new Bar(1,2);
delete b;

And the result will be:

Output

Foo::Foo(): 4 7

Accessing the Overridden Base Class Function

If in the inherited class a method is overridden, you can still access this member function as it is implemented in the base class using the following syntax:
<base class name>::<overridden function name>

Source code (UnigineScript)

class Foo {
	void foo(int a) {
		log.message("Foo::foo(): %d\n",a);
	}
};

class Bar : Foo {
	void foo(int a) {
		// Overridden method implementation
		log.message("Bar::foo(): %d\n",a + 3);
		// Accessing the base class method implementation
		Foo::foo(a);
   }
};

Bar b = new Bar();
b.foo(2);
delete b;

And the result will be:

Output

Bar::foo(): 5
Foo::foo(): 2

Creating Abstract Methods in a Base Class

You can create an abstract method in the base class and implement it in the derived one. However, in the base class method an error or, if necessary, an exception should be thrown. It is used to indicate that a method implementation is lacking in the derived class.

Source code (UnigineScript)

class Foo {
	void foo(int a) {
		log.error("Foo::foo(): pure virtual function call\n");	
	}
};

class Bar : Foo {
	void foo(int a) {
		int num = a + 5;
		log.message("Bar::foo(): %d\n",num);
   }
};

Bar b = new Bar();
b.foo(2);
delete b;

And the result will be:

Output

Bar::foo(): 7

Casting

An object of a parent polymorphic class can be cast to a child one, so as to access all its member functions.

Source code (UnigineScript)

class Foo {
    void foo() { }
};
int foo = new Foo();
Foo(foo).foo();  // changes a variable type
foo.foo();       // this is invalid

Class Based Branching

The fast class based branching can be implemented by using the switch-case conditional statement.

If you have several classes defined in the script and their instances require to be processed differently, you can use the classid() function as a constant for the case within the switch to check if the passed value is an instance of the particular class.

Source code (UnigineScript)

class Foo { };
class Bar { };
void foo(int a) {
  switch(classid(a)) {
    case classid(Foo): log.message("Foo\n"); break;
    case classid(Bar): log.message("Bar\n"); break;
    case classid(File): log.message("File\n"); break;
  }
}
foo(new Foo());
foo(new Bar());
foo(new File());

Output

Foo
Bar
File

To check that the classid() function returns the same ID for class and its instance, perform the following:

Source code (UnigineScript)

log.message("%d %d\n",classid(new Foo()),classid(Foo));
log.message("%d %d\n",classid(new Bar()),classid(Bar));
log.message("%d %d\n",classid(new File()),classid(File));

The example produces the following output:

Output

0 0
65536 65536
-6 -6

Inheritance from C++ Classes

User classes can not only be inherited from other user classes, but also from C++ classes:

Engine base classes (any classes from the core and UnigineScript libraries)
Extern C++ classes accessed via C++ API

In both of these cases, class inheritance is performed in the same way (see an example below).

Inheritance from Engine Classes

Here is an example how to create MyObjectMesh class which inherits from the base engine ObjectMeshStatic class.

Objects of the derived class can call methods of base class directly.
When passing object of the derived class to function that takes an object of the base class, inherited class cannot be automatically converted to the base class. Upcasting should be done explicitly via accessing extern member of the derived class.
To downcast the instance of base class to your custom derived class, use cast() function. This function is created automatically for all inherited classes and needs not to be implemented manually.

Source code (UnigineScript)

// Custom class inherited from base engine class.
class MyObjectMesh : ObjectMesh {
	int number;
	
	// Constructor.
	MyObjectMesh(string name, int a) : ObjectMesh(name) {
		number = a;
		log.message("MyObjectMesh object constructed\n");
	}
};

void foo(MyObjectMesh mesh) { 
	// Check if the argument is an instance of MyObjectMesh.
	if(is_base_class("MyObjectMesh",mesh) == 0) log.message("Object is not MyObjectMesh\n");
	else log.message("Object is MyObjectMesh\nNumber = %d\n", mesh.number);
		
	return;
};


/*
*/
MyObjectMesh mesh = new MyObjectMesh("samples/common/meshes/box.mesh",42);

// You can call functions of base class.
log.message("Mesh name: %s\n",mesh.getMeshName());

// To upcast the object to the base class, use "extern". 
// It's necessary when passing MyObjectMesh to a function that takes a base ObjectMesh or Node.
engine.world.isNode(mesh.extern));

// To downcast the object back to its derived class, use cast() function.
foo(MyObjectMesh::cast(mesh.extern));

The result will be:

Output

MyObjectMesh object constructed
Mesh name: samples/common/meshes/box.mesh
Object is MyObjectMesh
Number = 42

Using Callbacks in Inherited Classes

To use callbacks in the inherited class, you need to pass a reference to this class ( this) as an additional argument for the callback function.

For example, a callback in the class inherited from WidgetButton:

Source code (UnigineScript)

class MyButton : WidgetButton {
  private:
  
    void on_click(MyButton button) {
      log.message("on_click: %s\n",typeinfo(button));
    }
    
  public:
    
    MyButton(Gui gui) {
      extern = new WidgetButton(gui);
      extern.setCallback(GUI_CLICKED,"::MyButton::on_click",this);
    }
};

Here is another example with a class inherited from WorldTrigger:

Source code (UnigineScript)

class MyTrigger : WorldTrigger {
  private:
    
    void on_enter(Node node,MyTrigger trigger) {
      log.message("on_enter: %s %s\n",typeinfo(node),typeinfo(trigger));
    }

    void on_leave(Node node,MyTrigger trigger) {
      log.message("on_leave: %s %s\n",typeinfo(node),typeinfo(trigger));
    }
    
  public:
    
    MyTrigger(vec3 size) {
      extern = new WorldTrigger(size);
      extern.setEnterCallback("::MyTrigger::on_enter",this);
      extern.setLeaveCallback("::MyTrigger::on_leave",this);
    }
};

Function Chaining

In UnigineScript, function chaining enables to call a chain of functions in one statement. The return value of the first function is used to call the second function. Such approach is useful when there is no need to store intermediate objects. For example:

Source code (UnigineScript)

mesh.getBoundBox().getMin();

First the mesh.getBoundBox() is executed and an instance of the BoundBox class is returned. On this returned value the getMin() member function is called.

NoticeThe type of the return variable is equal to the return type of the last executed function.

Function chaining can also be used when calling functions of user-defined classes. For example:

Source code (UnigineScript)

// the 1st user defined class
class Foo {
    void print() { log.message(__FUNC__ + ": called\n"); }
};

// the 2nd user defined class
class Bar {
    Foo get_foo() { return new Foo(); }
};

int init() {
    // create an instance of the 2nd class
    Bar b = new Bar(); 
    // chain the function calls: call the get_foo() member function for the instance of the Bar class 
	// and then call the member function of the Foo class
	b.get_foo().print();
}
// Output: Foo::print(): called

Last update: 2018-08-10

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Object Oriented Programming

In This Article:

Classes

UnigineScript Class Types

Engine Classes

User-Defined Classes

External Classes

Access Specifiers

Constructors and Destructors

Constructors and new

Destructors and delete

Overloading

Function Overloading

Operator Overloading

Keywords

this Keyword

super Keyword

Inheritance

Calling the Base Class Constructor

Accessing the Overridden Base Class Function

Creating Abstract Methods in a Base Class

Casting

Class Based Branching

Inheritance from C++ Classes

Inheritance from Engine Classes

Using Callbacks in Inherited Classes

Function Chaining