The Ring programming language version 1.8 book - Part 36 of 202
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This document provides examples and explanations of object-oriented programming concepts in Ring including: defining classes with attributes and methods, instantiating objects, operator overloading, inheritance, dynamic attributes, packages, printing objects, finding objects in lists, sorting lists of objects, using self/this, default attribute values, and more. Key OOP concepts like encapsulation, abstraction, and polymorphism are demonstrated through multiple examples.
![Ring Documentation, Release 1.8
Func operator cOperator,Para
...
The function operator takes two paramters, the first represent the operator and the second represent the second param-
eter 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
42.6. Operator Overloading 322](https://image.slidesharecdn.com/351ring-180826100818/85/The-Ring-programming-language-version-1-8-book-Part-36-of-202-2-320.jpg)
![Ring Documentation, Release 1.8
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 & operator to return the item
values like strings an numbers by reference, so we can update it when we access the items.
42.7 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 the super object.
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
42.8 Dynamic Attributes
We can write instructions after the class name to be executed when we create new objects
Example:
42.7. Inheritance 323](https://image.slidesharecdn.com/351ring-180826100818/85/The-Ring-programming-language-version-1-8-book-Part-36-of-202-3-320.jpg)
![Ring Documentation, Release 1.8
42.10 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
42.11 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
42.10. Printing Objects 325](https://image.slidesharecdn.com/351ring-180826100818/85/The-Ring-programming-language-version-1-8-book-Part-36-of-202-5-320.jpg)
![Ring Documentation, Release 1.8
0
0
42.12 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
42.12. Sort() and List of Objects 326](https://image.slidesharecdn.com/351ring-180826100818/85/The-Ring-programming-language-version-1-8-book-Part-36-of-202-6-320.jpg)
The Ring programming language version 1.8 book - Part 36 of 202
- 1. Ring Documentation, Release 1.8 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 42.6 Operator Overloading We can add the operator method to our class to enable using operators with the class objects. Syntax: Class ClassName ... 42.6. Operator Overloading 321
- 2. Ring Documentation, Release 1.8 Func operator cOperator,Para ... The function operator takes two paramters, the first represent the operator and the second represent the second param- eter 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 42.6. Operator Overloading 322
- 3. Ring Documentation, Release 1.8 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 & operator to return the item values like strings an numbers by reference, so we can update it when we access the items. 42.7 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 the super object. 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 42.8 Dynamic Attributes We can write instructions after the class name to be executed when we create new objects Example: 42.7. Inheritance 323
- 4. Ring Documentation, Release 1.8 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 42.9 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 42.9. Packages 324
- 5. Ring Documentation, Release 1.8 42.10 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 42.11 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 42.10. Printing Objects 325
- 6. Ring Documentation, Release 1.8 0 0 42.12 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 42.12. Sort() and List of Objects 326
- 7. Ring Documentation, Release 1.8 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 42.13 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() 42.13. Using Self.Attribute and Self.Method() 327
- 8. Ring Documentation, Release 1.8 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 you typed the class attributes with self.attribute 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 Whay 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 42.14 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 42.14. Using This.Attribute and This.Method() 328
- 9. Ring Documentation, Release 1.8 42.15 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. 42.15. Using This in the class region as Self 329
- 10. Ring Documentation, Release 1.8 42.16 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 42.16. Default value for object attributes 330