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  <div class="section" id="object-oriented-programming-oop">
<h1>Object Oriented Programming (OOP)<a class="headerlink" href="#object-oriented-programming-oop" title="Permalink to this headline">¶</a></h1>
<p>In this chapter we are going to learn how to use the Object-Oriented programming paradigm
inside the Ring programming language.</p>
<p>We will learn about</p>
<ul class="simple">
<li>Classes and Objects</li>
<li>Access Objects Using Braces</li>
<li>Composition</li>
<li>Setter and Getter</li>
<li>Private Attributes and Methods</li>
<li>Operator Overloading</li>
<li>Inheritance</li>
<li>Dynamic Attributes</li>
<li>Packages</li>
</ul>
<div class="section" id="classes-and-objects">
<span id="index-0"></span><h2>Classes and Objects<a class="headerlink" href="#classes-and-objects" title="Permalink to this headline">¶</a></h2>
<p>We can define new classes using the next syntax</p>
<p>Syntax:</p>
<div class="highlight-none"><div class="highlight"><pre>Class &lt;Class Name&gt; [From &lt;Parent Class Name&gt;]
        [Attributes]
        [Methods]
        [Private
          [Attributes]
          [Methods]
        ]
</pre></div>
</div>
<p>And we can create objects using the next syntax</p>
<p>Syntax:</p>
<div class="highlight-none"><div class="highlight"><pre>New &lt;Object Name&gt; [ (init method parameters) ] |
                  [ { access object data and methods } ]   ---&gt; Object
</pre></div>
</div>
<p>Example:</p>
<div class="highlight-none"><div class="highlight"><pre>New point { x=10  y=20  z=30  print() }
Class Point x y z func print see x + nl + y + nl + z + nl
</pre></div>
</div>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">We can use { } to access object data and methods.</p>
</div>
<div class="admonition tip">
<p class="first admonition-title">Tip</p>
<p class="last">we can declare the class attributes directly after the class name.</p>
</div>
<p>Output:</p>
<div class="highlight-none"><div class="highlight"><pre>10
20
30
</pre></div>
</div>
<p>We can rewrite the same program in another style</p>
<div class="highlight-none"><div class="highlight"><pre>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 &amp; 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
</pre></div>
</div>
<p>Also we can write the same program in another way</p>
<div class="highlight-none"><div class="highlight"><pre>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
</pre></div>
</div>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">we can use the dot operator after the object name to access object members.</p>
</div>
<p>Also we can write the same program in another way</p>
<div class="highlight-none"><div class="highlight"><pre>new point { print() }
Class Point
        x = 10  y = 20  z = 30
        func print see x + nl + y + nl + z + nl
</pre></div>
</div>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">we can set the default values for the class attributes when we declare them.</p>
</div>
<p>Also we can write the same program in another way</p>
<div class="highlight-none"><div class="highlight"><pre>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
</pre></div>
</div>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">we can call the init method directly using () when we create new objects</p>
</div>
<p>Also we can write the same program in another way</p>
<div class="highlight-none"><div class="highlight"><pre>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
</pre></div>
</div>
<div class="admonition tip">
<p class="first admonition-title">Tip</p>
<p class="last">using Hash for passing method parameters enable us to create optional
parameters and change the order of parameters when adding them to the Hash.</p>
</div>
</div>
<div class="section" id="access-objects-using-braces">
<h2>Access Objects Using Braces<a class="headerlink" href="#access-objects-using-braces" title="Permalink to this headline">¶</a></h2>
<p>We can access the object at any time using braces { }</p>
<p>Inside the braces we can use the object attributes and methods directly</p>
<p>This can be done when we create the object using the New keyword or at any time using the next syntax</p>
<div class="highlight-none"><div class="highlight"><pre>ObjectName { access object data and methods }
</pre></div>
</div>
<p>Example:</p>
<div class="highlight-none"><div class="highlight"><pre>See &quot;Creating the Object&quot; + nl
o1 = new Point
See &quot;Using the Object&quot; + nl
o1 {
        x=5
        y=15
        z=25
        print()
}
Class Point x y z func print see x + nl + y + nl + z
</pre></div>
</div>
<p>We can use braces to access objects when we call functions or methods</p>
<p>Example:</p>
<div class="highlight-none"><div class="highlight"><pre>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
</pre></div>
</div>
<p>We can mix between using braces and the dot operator to access the object in the same expression.</p>
<p>Example:</p>
<div class="highlight-none"><div class="highlight"><pre>o1 = new Point

O1 { x=10 y=20 z=30 }.print()

Class Point x y z
        func print see x + nl + y + nl + z
</pre></div>
</div>
</div>
<div class="section" id="composition">
<h2>Composition<a class="headerlink" href="#composition" title="Permalink to this headline">¶</a></h2>
<p>The object may contains other objects as attributes.</p>
<p>Using braces to access objects can be nested.</p>
<p>Example:</p>
<div class="highlight-none"><div class="highlight"><pre>R1 = New Rectangle
{

        Name = &quot;Rectangle 1&quot;

        P1
        {
                X = 10
                Y = 20
        }

        P2
        {
                X = 200
                Y = 300
        }

        Color = &quot;Blue&quot;

}

see &quot;Name : &quot; + R1.Name + nl +
    &quot;Color: &quot; + R1.Color + nl +
    &quot;P1   : (&quot; + R1.P1.X + &quot;,&quot; + R1.P1.Y + &quot;)&quot; + nl +
    &quot;P2   : (&quot; + R1.P2.X + &quot;,&quot; + R1.P2.Y + &quot;)&quot;

Class Rectangle
        name  color
        p1 = new Point
        p2 = new Point

Class Point x y
</pre></div>
</div>
<p>Output:</p>
<div class="highlight-none"><div class="highlight"><pre>Name : Rectangle 1
Color: Blue
P1   : (10,20)
P2   : (200,300)
</pre></div>
</div>
</div>
<div class="section" id="setter-and-getter">
<h2>Setter and Getter<a class="headerlink" href="#setter-and-getter" title="Permalink to this headline">¶</a></h2>
<p>We can define methods to be used when we set and get object attributes.</p>
<p>Syntax:</p>
<div class="highlight-none"><div class="highlight"><pre>Class ClassName

        AttributeName
        ...

        Func SetAttributeName
                ...

        Func GetAttributeName
                ...
</pre></div>
</div>
<p>Example:</p>
<div class="highlight-none"><div class="highlight"><pre>o1 = new person

o1.name = &quot;Mahmoud&quot;  see o1.name + nl

o1 { name = &quot;Ahmed&quot;  see name }

Class Person

        name family = &quot;Fayed&quot;

        func setname value
                see &quot;Message from SetName() Function!&quot; + nl
                name = value + &quot; &quot; + family

        func getname
                see &quot;Message from GetName() Function!&quot; + nl
                return &quot;Mr. &quot; + name
</pre></div>
</div>
<p>Output:</p>
<div class="highlight-none"><div class="highlight"><pre>Message from SetName() Function!
Message from GetName() Function!
Mr. Mahmoud Fayed
Message from SetName() Function!
Message from GetName() Function!
Mr. Ahmed Fayed
</pre></div>
</div>
</div>
<div class="section" id="private-attributes-and-methods">
<h2>Private Attributes and Methods<a class="headerlink" href="#private-attributes-and-methods" title="Permalink to this headline">¶</a></h2>
<p>We can define private attributes and methods after the keyword private inside the class body</p>
<p>Example:</p>
<div class="highlight-none"><div class="highlight"><pre>o1 = new person {
        name = &quot;Test&quot;
        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 &quot;Name   : &quot; + name + nl +
                    &quot;Age    : &quot; + age + nl

        func printsalary
                see &quot;Salary : &quot; + salary + nl

        private

        salary = 15000

        func increasesalary x
                salary += x
</pre></div>
</div>
<p>Output:</p>
<div class="highlight-none"><div class="highlight"><pre>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
</pre></div>
</div>
</div>
<div class="section" id="operator-overloading">
<h2>Operator Overloading<a class="headerlink" href="#operator-overloading" title="Permalink to this headline">¶</a></h2>
<p>We can add the operator method to our class to enable using operators with the class objects.</p>
<p>Syntax:</p>
<div class="highlight-none"><div class="highlight"><pre>Class ClassName

        ...

        Func operator cOperator,Para

                ...
</pre></div>
</div>
<p>The function operator takes two paramters, the first represent the operator
and the second represent the second parameter after the operator.</p>
<p>Example:</p>
<div class="highlight-none"><div class="highlight"><pre>o1 = new point { x = 10 y = 10 print(&quot;P1    : &quot;) }
o2 = new point { x = 20 y = 40 print(&quot;P2    : &quot;) }

o3 = o1 + o2
o3.print(&quot;P1+P2 : &quot;)

class point x y

        func operator cOperator,Para
                result = new point
                switch cOperator
                on &quot;+&quot;
                        result.x = x + Para.x
                        result.y = y + Para.y
                on &quot;-&quot;
                        result.x = x - Para.x
                        result.y = y - Para.y
                off
                return result

        func print cPoint
                see cPoint + &quot;X : &quot; + x + &quot; Y : &quot; + y + nl
</pre></div>
</div>
<p>Output:</p>
<div class="highlight-none"><div class="highlight"><pre>P1    : X : 10 Y : 10
P2    : X : 20 Y : 40
P1+P2 : X : 30 Y : 50
</pre></div>
</div>
</div>
<div class="section" id="inheritance">
<h2>Inheritance<a class="headerlink" href="#inheritance" title="Permalink to this headline">¶</a></h2>
<p>We can create class from another class in the class definition using the keyword from.</p>
<p>Syntax:</p>
<div class="highlight-none"><div class="highlight"><pre>Class &lt;Class Name&gt; [From &lt;Parent Class Name&gt;]
</pre></div>
</div>
<p>We can call a method in the parent class from the child class using the super object.</p>
<p>Syntax:</p>
<div class="highlight-none"><div class="highlight"><pre>func methodname
        ...
        super.methodname()
        ...
</pre></div>
</div>
<p>Example:</p>
<div class="highlight-none"><div class="highlight"><pre>Func main
        e1 = new Employee {
                Name = &quot;test&quot;
                age = 20
                job = &quot;programmer&quot;
                salary = 20000000
                print()
        }


Class Human
        Name Age
        func print
                see &quot;Name : &quot; + name + nl + &quot;Age  : &quot; + age + nl

Class Employee from Human
        Job Salary
        func print
                super.print()
                see &quot;Job  : &quot; + job + nl + &quot;Salary : &quot; + salary + nl
</pre></div>
</div>
<p>Output:</p>
<div class="highlight-none"><div class="highlight"><pre>Name : test
Age  : 20
Job  : programmer
Salary : 20000000
</pre></div>
</div>
</div>
<div class="section" id="dynamic-attributes">
<h2>Dynamic Attributes<a class="headerlink" href="#dynamic-attributes" title="Permalink to this headline">¶</a></h2>
<p>We can write instructions after the class name to be executed when we create new objects</p>
<p>Example:</p>
<div class="highlight-none"><div class="highlight"><pre>o1 = new dynamicClass
see o1.var5 + nl        # output 5

Class DynamicClass
        for x = 1 to 10
                cStr = &quot;var&quot; + x + &quot; = &quot; + x
                eval(cStr)
        next
</pre></div>
</div>
<div class="admonition tip">
<p class="first admonition-title">Tip</p>
<p class="last">in the previous example var1, var2, ..., var10 will be defined as attributes.</p>
</div>
<div class="admonition tip">
<p class="first admonition-title">Tip</p>
<p class="last">The problem with the previous example is that x and cStr will be defined as attributes too!</p>
</div>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">we can write class definitions inside a string then
using eval() we can execute the string to define the classes</p>
</div>
</div>
<div class="section" id="packages">
<h2>Packages<a class="headerlink" href="#packages" title="Permalink to this headline">¶</a></h2>
<p>We can create a package (a group of classes under a common name) using the next syntax</p>
<div class="highlight-none"><div class="highlight"><pre>package PackageName
        Class Class1
                ...
        Class Class2
                ...
        Class Class3
                ...
        ...
</pre></div>
</div>
<p>Example</p>
<div class="highlight-none"><div class="highlight"><pre>o1 = new System.output.console
o1.print(&quot;Hello World&quot;)

Package System.Output
        Class Console
                Func Print cText
                        see cText + nl
</pre></div>
</div>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">we can use the dot operator as part of the package name</p>
</div>
<p>Instead of typing the long name PackageName.ClassName we can use the import command</p>
<p>When we import a package, we can use any class inside this package directly.</p>
<p>Example</p>
<div class="highlight-none"><div class="highlight"><pre>import system.output
o1 = new console {
        print(&quot;Hello World&quot;)
}
Package System.Output
        Class Console
                Func Print cText
                        see cText + nl
</pre></div>
</div>
</div>
<div class="section" id="printing-objects">
<h2>Printing Objects<a class="headerlink" href="#printing-objects" title="Permalink to this headline">¶</a></h2>
<p>We can print the object state (attributes and values) using the see command.</p>
<p>Example:</p>
<div class="highlight-none"><div class="highlight"><pre>see new point { x=10 y=20 z=30 }
class point x y z
</pre></div>
</div>
<p>Output:</p>
<div class="highlight-none"><div class="highlight"><pre>x: 10.000000
y: 20.000000
z: 30.000000
</pre></div>
</div>
</div>
</div>


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  <h3><a href="index.html">Table Of Contents</a></h3>
  <ul>
<li><a class="reference internal" href="#">Object Oriented Programming (OOP)</a><ul>
<li><a class="reference internal" href="#classes-and-objects">Classes and Objects</a></li>
<li><a class="reference internal" href="#access-objects-using-braces">Access Objects Using Braces</a></li>
<li><a class="reference internal" href="#composition">Composition</a></li>
<li><a class="reference internal" href="#setter-and-getter">Setter and Getter</a></li>
<li><a class="reference internal" href="#private-attributes-and-methods">Private Attributes and Methods</a></li>
<li><a class="reference internal" href="#operator-overloading">Operator Overloading</a></li>
<li><a class="reference internal" href="#inheritance">Inheritance</a></li>
<li><a class="reference internal" href="#dynamic-attributes">Dynamic Attributes</a></li>
<li><a class="reference internal" href="#packages">Packages</a></li>
<li><a class="reference internal" href="#printing-objects">Printing Objects</a></li>
</ul>
</li>
</ul>

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