The Ring programming language version 1.7 book - Part 34 of 196

Ring Documentation, Release 1.7
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.
new point { print() }
Class Point
x = 10 y = 20 z = 30
func print see x + nl + y + nl + z + nl
41.1. Classes and Objects 302

Note: we can set the default values for the class attributes when we declare them.
new point(10,20,30)
Class Point
x y z
func init p1,p2,p3 x=p1 y=p2 z=p3 print()
Note: we can call the init method directly using () when we create new objects
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()
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.
41.2 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 +
41.2. Access Objects Using Braces 303

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
41.3 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:
41.3. Composition 304

Name : Rectangle 1
Color: Blue
P1 : (10,20)
P2 : (200,300)
41.4 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
41.5 Private Attributes and Methods
We can deﬁne private attributes and methods after the keyword private inside the class body
41.4. Setter and Getter 305

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
41.6 Operator Overloading
We can add the operator method to our class to enable using operators with the class objects.
Syntax:
Class ClassName
...
41.6. Operator Overloading 306

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
41.6. Operator Overloading 307

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.
41.7 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
41.8 Dynamic Attributes
We can write instructions after the class name to be executed when we create new objects
Example:
41.7. Inheritance 308

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
41.9 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
41.9. Packages 309

41.10 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
41.11 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
class company position name symbol
Output:
2
3
1
3
1
2
1
3
Other
0
41.10. Printing Objects 310

0
0
41.12 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
41.12. Sort() and list of objects 311

The Ring programming language version 1.7 book - Part 34 of 196

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The Ring programming language version 1.7 book - Part 34 of 196