Object Oriented Programming (OOP)
In this chapter we are going to learn how to use the Object-Oriented programming paradigm inside the Ring programming language.
We will learn about
Classes and Objects
Access Objects Using Braces
Composition
Setter and Getter
Private Attributes and Methods
Operator Overloading
Inheritance
Dynamic Attributes
Packages
Printing Objects
Find() and List of Objects
Sort() and List of Objects
Using Self.Attribute and Self.Method()
Using This.Attribute and This.Method()
Command: New From
Classes and Objects
We can define new classes using the next syntax
Syntax:
Class <Class Name> [From|<|: <Parent Class Name>] [Attributes] [Methods] [Private [Attributes] [Methods] ] And we can create objects using the next syntax
Syntax:
New <Object Name> [ (init method parameters) ] | [ { access object data and methods } ] ---> Object Example:
New point { x=10 y=20 z=30 print() } Class Point x y z func print see x + nl + y + nl + z + nl Note
We can use { } to access object data and methods.
Tip
we can declare the class attributes directly after the class name.
Output:
10 20 30 We can rewrite the same program in another style
New point # create new object using the point class { # access the new object attributes and methods x = 10 # set the x attribute to 10 y = 20 # set the y attribute to 20 z = 30 # set the z attribute to 30 print() # call the print method } # end of object access Class Point # define the Point class x y z # the class contains three attributes x, y & z func print # define the print method see x + nl + # print the x attribute y + nl + # print the y attribute z + nl # print the z attribute Also we can write the same program in another way
P1 = New Point P1.x = 10 P1.y = 20 P1.z = 30 P1.Print() Class Point x y z func print see x + nl + y + nl + z + nl Note
we can use the dot operator after the object name to access object members.
Also we can write the same program in another way
new point { print() } Class Point x = 10 y = 20 z = 30 func print see x + nl + y + nl + z + nl Note
we can set the default values for the class attributes when we declare them.
Also we can write the same program in another way
new point(10,20,30) Class Point x y z func init p1,p2,p3 x=p1 y=p2 z=p3 print() func print see x + nl + y + nl + z + nl Note
we can call the init method directly using () when we create new objects
Also we can write the same program in another way
new point( [ :x = 10 , :y = 20 , :z = 30 ] ) Class Point x y z func init aPara x = aPara[:x] y = aPara[:y] z = aPara[:z] print() func print see x + nl + y + nl + z + nl Tip
using Hash for passing method parameters enable us to create optional parameters and change the order of parameters when adding them to the Hash.
Access Objects Using Braces
We can access the object at any time using braces { }
Inside the braces we can use the object attributes and methods directly
This can be done when we create the object using the New keyword or at any time using the next syntax
ObjectName { access object data and methods } Example:
See "Creating the Object" + nl o1 = new Point See "Using the Object" + nl o1 { x=5 y=15 z=25 print() } Class Point x y z func print see x + nl + y + nl + z We can use braces to access objects when we call functions or methods
Example:
o1 = new Point print( o1 { x=10 y=20 z=30 } ) func print object see object.x + nl + object.y + nl + object.z Class Point x y z We can mix between using braces and the dot operator to access the object in the same expression.
Example:
o1 = new Point O1 { x=10 y=20 z=30 }.print() Class Point x y z func print see x + nl + y + nl + z Composition
The object may contains other objects as attributes.
Using braces to access objects can be nested.
Example:
R1 = New Rectangle { Name = "Rectangle 1" P1 { X = 10 Y = 20 } P2 { X = 200 Y = 300 } Color = "Blue" } see "Name : " + R1.Name + nl + "Color: " + R1.Color + nl + "P1 : (" + R1.P1.X + "," + R1.P1.Y + ")" + nl + "P2 : (" + R1.P2.X + "," + R1.P2.Y + ")" Class Rectangle name color p1 = new Point p2 = new Point Class Point x y Output:
Name : Rectangle 1 Color: Blue P1 : (10,20) P2 : (200,300) Setter and Getter
We can define methods to be used when we set and get object attributes.
Syntax:
Class ClassName AttributeName ... Func SetAttributeName ... Func GetAttributeName ... Example:
o1 = new person o1.name = "Mahmoud" see o1.name + nl o1 { name = "Ahmed" see name } Class Person name family = "Fayed" func setname value see "Message from SetName() Function!" + nl name = value + " " + family func getname see "Message from GetName() Function!" + nl return "Mr. " + name Output:
Message from SetName() Function! Message from GetName() Function! Mr. Mahmoud Fayed Message from SetName() Function! Message from GetName() Function! Mr. Ahmed Fayed Private Attributes and Methods
We can define private attributes and methods after the keyword private inside the class body
Note
A subclass could access private attributes/methods defined in the parent class.
Tip
Once we create an object, no other object (even from the same class) could access it’s private attributes/methods directly.
Example:
o1 = new person { name = "Test" age = 20 print() o1.printsalary() } try see o1.salary catch see cCatchError + nl done try o1.increasesalary(1000) catch see cCatchError + nl done Class Person name age func print see "Name : " + name + nl + "Age : " + age + nl func printsalary see "Salary : " + salary + nl private salary = 15000 func increasesalary x salary += x Output:
Name : Test Age : 20 Salary : 15000 Error (R27) : Using private attribute from outside the class : salary Error (R26) : Calling private method from outside the class : increasesalary Operator Overloading
We can add the operator method to our class to enable using operators with the class objects.
Syntax:
Class ClassName ... Func operator cOperator,Para ... The function operator takes two parameters, the first represent the operator and the second represent the second parameter after the operator.
Example:
o1 = new point { x = 10 y = 10 print("P1 : ") } o2 = new point { x = 20 y = 40 print("P2 : ") } o3 = o1 + o2 o3.print("P1+P2 : ") class point x y func operator cOperator,Para result = new point switch cOperator on "+" result.x = x + Para.x result.y = y + Para.y on "-" result.x = x - Para.x result.y = y - Para.y off return result func print cPoint see cPoint + "X : " + x + " Y : " + y + nl Output:
P1 : X : 10 Y : 10 P2 : X : 20 Y : 40 P1+P2 : X : 30 Y : 50 The next example from the List class in the stdlib.ring
Func operator cOperator,Para result = new list switch cOperator on "+" if isobject(para) for t in Para.vValue vValue + t next but islist(para) for t in Para vValue + t next ok on "len" return len( vValue ) on "[]" return &vValue[para] off return result The “len” operator is used with (for in) control structure.
The “[]” operator is used when we try to access the list items, In this case we use the (return &) command to return the item values like strings and numbers by reference, so we can update it when we access the items.
Another Example
func main See "----1"+nl a1 = new BigNumber( "123" ) a2 = new BigNumber( "456" ) a3 = new BigNumber( "789" ) See nl+"----2"+nl a1.print() a2.print() a3.print() See nl+"----3"+nl a2 = a1 + "45" See nl+"----4"+nl a2.print() See nl+"----5"+nl a3 = a1 + a2 See nl+"----6"+nl a3.print() See nl+"----7"+nl ###================================== Func FuncAdd( num1, num2) Sum = 0 + num1 + num2 ### Para.aData isNumber Sum = "" +Sum ### Para.adata isString return Sum ### return to Class ###=================================== class BigNumber ### Variables aData = "468" ### Functions INIT default values func init aPara ? "INIT aPara: " ? aPara if isString(aPara) aData = aPara else aData = "" + aPara ok ### Other Functions func operator cOperator, Para whatType = Type(Para) ? nl+"WhatType-PARA: "+ whatType ? Para ? nl+"Operator: " ? cOperator ? nl+"PARA: " ? Para ? " ______" ? nl if whatType = "STRING" dataInfo = Para ? "dataInfo String: " ? dataInfo but whatType = "NUMBER" datinfo = "" + Para ? "dataInfo Number: " ? dataInfo else whatType = "OBJECT" dataInfo = "" + para.aData ? "dataInfo OBJECT: " ? dataInfo ok ? "dataInfo USING: " ? dataInfo ### Para.aData does NOT exist on first pass ( Object with member) ### Result isObject when assigned "self" result = self switch cOperator on "+" answer = FuncAdd( aData, dataInfo ) ? nl+"AnswerString - FunAdd aData, dataInfo: " ? answer ### result = self, is Object, populate Object with aData member result.aData = answer off ### Result = Self is Object return result func print ? nl+"ClassPrint aData: " ? aData Starting from Ring 1.21, We support that the value could come first before the object and the operator() method will be called but the letter ‘r’ will comes before the operator (i.e. r+ instead of +)
Example:
? f(2) mylist = new List([1,2,3]) f(mylist).print() func f x return 2+x*x # Here 2 comes before x and x could be an object class List aList = [] func init vValue aList = vValue func operator cOperator,vValue if cOperator = "r+" cOperator = "+" ok switch cOperator on "+" if isNumber(vValue) { for t in aList t += vValue next but isObject(vValue) for t = 1 to len(aList) aList[t] += vValue[t] next ok on "*" if isNumber(vValue) { for t in aList t *= vValue next but isObject(vValue) for t = 1 to len(aList) aList[t] *= vValue[t] next ok on "[]" return aList[vValue] on "len" return len(aList) off return self func print ? aList Output:
6 3 6 11 Note
the numbers(3,6,11) are the result of applying the function f to the list items [1,2,3]
Inheritance
We can create class from another class in the class definition using the keyword from.
Syntax:
Class <Class Name> [From <Parent Class Name>] We can call a method in the parent class from the child class using Super.
Note
Super provide access to the methods only (No access to the attributes).
Tip
Using ParentClassName(self) we can know the parent class name or get an empty string if no parent class exists.
Syntax:
func methodname ... super.methodname() ... Example:
Func main e1 = new Employee { Name = "test" age = 20 job = "programmer" salary = 20000000 print() } Class Human Name Age func print see "Name : " + name + nl + "Age : " + age + nl Class Employee from Human Job Salary func print super.print() see "Job : " + job + nl + "Salary : " + salary + nl Output:
Name : test Age : 20 Job : programmer Salary : 20000000 Dynamic Attributes
We can write instructions after the class name to be executed when we create new objects
Example:
o1 = new dynamicClass see o1.var5 + nl # output 5 Class DynamicClass for x = 1 to 10 cStr = "var" + x + " = " + x eval(cStr) next Tip
in the previous example var1, var2, …, var10 will be defined as attributes.
Tip
The problem with the previous example is that x and cStr will be defined as attributes too!
Note
we can write class definitions inside a string then using eval() we can execute the string to define the classes
Packages
We can create a package (a group of classes under a common name) using the next syntax
package PackageName Class Class1 ... Class Class2 ... Class Class3 ... ... Example
o1 = new System.output.console o1.print("Hello World") Package System.Output Class Console Func Print cText see cText + nl Note
we can use the dot operator as part of the package name
Instead of typing the long name PackageName.ClassName we can use the import command
When we import a package, we can use any class inside this package directly.
Example
import system.output o1 = new console { print("Hello World") } Package System.Output Class Console Func Print cText see cText + nl Printing Objects
We can print the object state (attributes and values) using the see command.
Example:
see new point { x=10 y=20 z=30 } class point x y z Output:
x: 10.000000 y: 20.000000 z: 30.000000 Find() and List of Objects
We can use the find() function to search inside a list of objects.
Syntax:
Find(List,ItemValue,nColumn,cAttribute) ---> Item Index Example:
myList1 = [new Company {position=3 name="Mahmoud" symbol="MHD"}, new Company {position=2 name="Bert" symbol="BRT"}, new Company {position=1 name="Ring" symbol="RNG"} ] see find(mylist1,"Bert",1,"name") + nl see find(mylist1,"Ring",1,"name") + nl see find(mylist1,"Mahmoud",1,"name") + nl see find(mylist1,"RNG",1,"symbol") + nl see find(mylist1,"MHD",1,"symbol") + nl see find(mylist1,"BRT",1,"symbol") + nl see find(mylist1,3,1,"position") + nl see find(mylist1,1,1,"position") + nl see "Other" + nl see find(mylist1,"test",1,"name") + nl see find(mylist1,"test",0,"name") + nl see find(mylist1,"test",5,"name") + nl class company position name symbol Output:
2 3 1 3 1 2 1 3 Other 0 0 0 Sort() and List of Objects
We can sort a list of objects based on an object attribute using the Sort() function.
Syntax:
Sort(List,nColumn,cAttribute) ---> Sorted List based on Object Attribute Example:
myList1 = [ new Company {position=3 name="Mahmoud" symbol="MHD"}, new Company {position=2 name="Bert" symbol="BRT"}, new Company {position=8 name="Charlie" symbol="CHR"}, new Company {position=6 name="Easy" symbol="FEAS"}, new Company {position=7 name="Fox" symbol="EFOX"}, new Company {position=5 name="Dog" symbol="GDOG"}, new Company {position=4 name="George" symbol="DGRG"}, new Company {position=1 name="Ring" symbol="RNG"} ] see sort(mylist1,1,"name") see copy("*",70) + nl see sort(mylist1,1,"symbol") see copy("*",70) + nl see sort(mylist1,1,"position") class company position name symbol Output:
position: 2.000000 name: Bert symbol: BRT position: 8.000000 name: Charlie symbol: CHR position: 5.000000 name: Dog symbol: GDOG position: 6.000000 name: Easy symbol: FEAS position: 7.000000 name: Fox symbol: EFOX position: 4.000000 name: George symbol: DGRG position: 3.000000 name: Mahmoud symbol: MHD position: 1.000000 name: Ring symbol: RNG ********************************************************************** position: 2.000000 name: Bert symbol: BRT position: 8.000000 name: Charlie symbol: CHR position: 4.000000 name: George symbol: DGRG position: 7.000000 name: Fox symbol: EFOX position: 6.000000 name: Easy symbol: FEAS position: 5.000000 name: Dog symbol: GDOG position: 3.000000 name: Mahmoud symbol: MHD position: 1.000000 name: Ring symbol: RNG ********************************************************************** position: 1.000000 name: Ring symbol: RNG position: 2.000000 name: Bert symbol: BRT position: 3.000000 name: Mahmoud symbol: MHD position: 4.000000 name: George symbol: DGRG position: 5.000000 name: Dog symbol: GDOG position: 6.000000 name: Easy symbol: FEAS position: 7.000000 name: Fox symbol: EFOX position: 8.000000 name: Charlie symbol: CHR Using Self.Attribute and Self.Method()
Inside the class region (After the class name and before any method) and the class methods we can use self.attribute and self.method()
Class Point self.x = 10 self.y = 20 self.z = 30 func print see self.x + nl + self.y + nl + self.z + nl Note
using self.attribute in the class region to define the class attribute protect the class attributes from conflict with global variables.
Tip
if we defined the class attributes without using self or this and there are a global variable with the same name it will be used and the attribute will not be defined.
Check the “Scope Rules” chapter to know about the conflict between the global variable name and the attribute name
What this may happens?
Because
Because in the class region we can access global variables.
Before defining any variable, Ring try to find the variable and use it if it’s found.
Note
Try to avoid the global variables, use the main function and start their names with $
Tip
In large programs protect your classes and define their members using self.attribute
Tip
A better solution to avoid using self and this in the class region is to use different global scope and the load package command
Using This.Attribute and This.Method()
Inside class methods we have access to the object scope directly. we don’t need to use Self.attribute or Self.method to read/write attribute and call methods.
But we can use braces {} while we are inside methods to access another object, In this case the current object scope will be changed while we are inside the brace.
How we can get access to our class attributes and methods while we are inside braces?
This can be done using This.Attribute and This.Method()
Example:
new point class point x=10 y=20 z=30 print() func print new UI { display(this.x,this.y,this.z) } Class UI func display x,y,z see x + nl + y + nl + z + nl Using This in the class region as Self
The class region is the region that comes after the class name and before any method.
We can use This in the class region as Self.
Example:
func main o1 = new program { test() } ? o1 class program this.name = "My Application" this.version = "1.0" ? name ? version func test ? "Name = " + name ? "Version = " + version Output
My Application 1.0 Name = My Application Version = 1.0 name: My Application version: 1.0 Note
When we use braces to change the current active object, Using This we can still point to the class.
Tip
The difference between This and Self is that Self point to the current active object that we can change using braces.
Remember that in most cases we don’t need to use This or Self in the class region
We can write
class program name version Or
class program name="My Application" version="1.0" Note
We use This or Self in the class region just to avoid conflict with global variables that are defined with the same name.
Default value for object attributes
The default value for object attributes is NULL
In Ring, the NULL value is just an empty string or a string that contains “NULL”
We can check for NULL values using the isNULL() function
Example:
oProgram = new Program ? oProgram.name ? oProgram.version ? isNULL(oProgram.name) ? isNULL(oProgram.version) oProgram { name="My Application" version="1.0" } ? isNULL(oProgram.name) ? isNULL(oProgram.version) ? oProgram class program name version Output:
NULL NULL 1 1 0 0 name: My Application version: 1.0 Command: New From
Using (new) we can create a new object from a specific class
Using (new from) we provide a variable which contains the class name
Example:
cClassName = "myclass2" myobj = new from cClassName cClassName = "myclass" myobj = new from cClassName class myclass ? :hello class myclass2 ? :wow Output:
wow hello Using Objects During Definition
Starting from Ring 1.19, The language provides better support for using objects during definition where we can mix between this feature and other features like operator overloading without missing the output
Example:
The new point object will be stored directly in myVar during definition
We can pass myVar as parameter to the print() method
Using + 1 will call the operator() method
The operator() method output will be stored in myVar
This means that the Assignment operation is executed TWO TIMES!
The first Assignment is executed to support (Using objects during definition) where myVar is an object contains the new point while in the second time, the Assignment is executed to support storing the Operator Overloading output.
Note
RingQt samples uses this feature to quickly pass the parent window object to the other widgets.