<?xml version="1.0" encoding="big5"?>
 <chapter id="language.oop">
  <title>OM</title>

  <sect1 id="keyword.class">
   <title><literal>O</literal></title>
   <para>
    O²ӻNO@pq(]iO@jq)@ӦW٪{qA 䤺ܼƥHΨϥγoܼƪơC wqOykЬݤUCܽdG 
    <informalexample>
     <programlisting role="php">
&lt;?php
class Cart {
    var $items;  // Items in our shopping cart
   
    // Add $num articles of $artnr to the cart
 
    function add_item ($artnr, $num) {
        $this->items[$artnr] += $num;
    }
   
    // Take $num articles of $artnr out of the cart
 
    function remove_item ($artnr, $num) {
        if ($this->items[$artnr] > $num) {
            $this->items[$artnr] -= $num;
            return true;
        } else {
            return false;
        }   
    }
}
?&gt;
     </programlisting>
    </informalexample>
   </para>
 
   <para>
    WwqF@ӥs Cart O(: Wʪ)C ]AF@ӦWٯަ}CHӤOΨӦb}C[JΦ~ơC 
   </para>

   <note>
    <simpara>
     In PHP 4, only constant initializers for <literal>var</literal>
     variables are allowed. Use constructors for non-constant
     initializers.  
    </simpara>
    <informalexample>
     <programlisting role="php">
/* None of these will work in PHP 4. */
class Cart {
    var $todays_date = date("Y-m-d");
    var $name = $firstname;
    var $owner = 'Fred ' . 'Jones';
}

/* This is how it should be done. */
class Cart {
    var $todays_date;
    var $name;
    var $owner;

    function Cart() {
        $this->todays_date = date("Y-m-d");
        $this->name = $GLOBALS['firstname'];
        /* etc. . . */
    }
}
     </programlisting>
    </informalexample>
   </note>

   <para>
    OO@ܼƪκAC ]NO integerB string HYOκAܼơC POإ߬YOܼƻݭnΨ new O (: o˲ܼͪƳNyWsإߤF@Ӫ)G 
   </para>
 
   <informalexample>
    <programlisting role="php">
$cart = new Cart;
$cart->add_item("10", 1);
    </programlisting>
   </informalexample>
 
   <para>
    WҫإߤF@ӥs cart A OO $CartC (ٰOo PHP jpgO@˪ ?) ۽եθӪ󤤪 add_item Ʀb}C[J@ӽs '10' FC 
</para><para> O]iHOLOC sO~ӤFªO~٥iH[WۤvܼƤΥ\C wqOkOwqOɥ[W extend orC Lǩwh~YC 
   </para>
 
   <informalexample>
    <programlisting role="php">
class Named_Cart extends Cart {
    var $owner;
  
    function set_owner ($name) {
        $this->owner = $name;
    }
}
    </programlisting>
   </informalexample>
 
   <para>
    WswqF Named_Cart OA ֦ Cart OҦܼƤΨƥt[W@ӦsΤWrܼƤΦsܼƪơG set_owner()C AiΦѤkھڷsOإߤ@ӪA {boӪ󰣤FiHHe@˥[F~٥iH]wΤWrG 
   </para>
 
   <informalexample>
    <programlisting role="php">
$ncart = new Named_Cart;    // Create a named cart
$ncart->set_owner ("kris"); // Name that cart
print $ncart->owner;        // print the cart owners name
$ncart->add_item ("10", 1); // (inherited functionality from cart)
    </programlisting>
   </informalexample>
  
   <para>
   bwqO $this oܼƬO󥻨C b󤧤A@wn $this->something yӽեΩΦs󤤪ܼƩMơC 
C
Both in and
    outside of the object you do not need a $ when accessing an object's
    properties.
   </para>

   <informalexample>
    <programlisting role="php">
$ncart->owner  = "chris"; // no $

$ncart->$owner = "chris";
// this is invalid because $ncart->$owner = $ncart->""

$myvar = 'owner';
$ncart->$myvar = "chris";  
// this is valid because $ncart->$myvar = $ncart->owner
    </programlisting>
   </informalexample>

   <para>
    Constructors سy OO@ӨơC |bCӮھڸOͪɦ۰ʳQC ܦسy̨ƪkOӨƩRWMOWr@ˡC 
   </para>
 
   <informalexample>
    <programlisting role="php">
class Auto_Cart extends Cart {
    function Auto_Cart () {
        $this->add_item ("10", 1);
    }
}
    </programlisting>
   </informalexample>
 
   <para>
    Wڭ̩wqF Auto_Cart OC O@ Cart O[WF@ӫسy̨ơA oƷ|۰ʷ|b}C (Ϊ̻Oʪ) [W@ '10' FC t~سy̨Ƥ]iHѼơA oOإߪɦjuʡC 
   </para>
 
   <informalexample>
    <programlisting role="php">
class Constructor_Cart extends Cart {
    function Constructor_Cart ($item = "10", $num = 1) {
        $this->add_item ($item, $num);
    }
}
 
// Shop the same old boring stuff.
 
$default_cart   = new Constructor_Cart;
 
// Shop for real...
 
$different_cart = new Constructor_Cart ("20", 17);
    </programlisting>
   </informalexample>
 
   <caution>
    <simpara>
     ~OӨA pGlOMOسy̨ƸܡA إ~Oɨä|PɽեΥOسy̨ơC 
    </simpara> 
   </caution>
  </sect1>
  
 <sect1 id="language.oop.newref">
   <title>References inside the constructor</title>
   <para>
    Creating references within the constructor can lead to confusing
    results. This tutorial-like section helps you to avoid problems.
 
    <informalexample>
     <programlisting role="php">

class foo {
    function foo($name) {
        // create a reference inside the global array $globalref
        global $globalref;
		$globalref[] = &amp;$this;
        // set name to passed value
        $this->setName($name);
		// and put it out
        $this->echoName();
    }

    function echoName() {
        echo "&lt;br&gt;",$this->Name;
    }
	
	function setName($name)	{
		$this->Name = $name;
    }
}
    </programlisting>
   </informalexample>
  </para>
    
   <para>
   Let us check out if there is a difference between <varname>$bar1</varname> which has been created using the copy <literal>=</literal> operator
   and <varname>$bar2</varname> which has been created using the reference <literal>=&amp;</literal> operator...
   

    <informalexample>
     <programlisting role="php">
   
    $bar1 = new foo('set in constructor');
    $bar1->echoName();
    $globalref[0]->echoName();
    
    /* output:
    set in constructor
    set in constructor
    set in constructor */
    
    $bar2 =&amp; new foo('set in constructor');
    $bar2->echoName();
    $globalref[1]->echoName();

    /* output:
    set in constructor
    set in constructor
    set in constructor */
    
        </programlisting>
   </informalexample>
  </para>
   <para>
    Apparently there is no difference, but in fact there is a very significant one:
    <varname>$bar1</varname> and <varname>$globalref[0]</varname> are _NOT_ referenced, they are NOT the same variable. 
    This is because "new" does not return a reference by default, instead it returns a copy.
       <note>
         <simpara>
         There is no performance loss (since php 4 and up use reference counting) returning copies instead of references.
         On the contrary it is most often better to simply work with copies instead of references, because creating
         references takes some time where creating copies virtually takes no time (unless none of them is a large array or object
         and one of them gets changed and the other(s) one(s) subsequently, then it would be wise to use references to change them
         all concurrently).
         </simpara>
        </note>
    To prove what is written above let us watch the code below.
   

   <informalexample>
     <programlisting role="php">
        // now we will change the name. what do you expect?
        // you could expect that both $bar and $globalref[0] change their names...
        $bar1->setName('set from outside');

        // as mentioned before this is not the case.
        $bar1->echoName();
        $globalref[0]->echoName();

        /* output:
        set on object creation
        set from outside */

        // let us see what is different with $bar2 and $globalref[1]
        $bar2->setName('set from outside');

        // luckily they are not only equyl, they are thesame variable
        // thus $bar2->Name and $globalref[1]->Name are the same too
        $bar2->echoName();
        $globalref[1]->echoName();

        /* output:
        set from outside
        set from outside */
        
      </programlisting>
   </informalexample>   
 </para>   
   <para>
   Another final example, try to understand it.
   
   <informalexample>
     <programlisting role="php">

class a {
    function a($i) {
        $this->value = $i;
        // try to figure out why we do not need a reference here
        $this->b = new b($this);
    }

    function createRef() {
        $this->c = new b($this);
    }

    function echoValue() {
        echo "&lt;br&gt;","class ",get_class($this),': ',$this->value;
        }
}


class b  {

    function b(&amp;$a) {
        $this->a = &amp;$a;
    }

   function echoValue() {
        echo "&lt;br&gt;","class ",get_class($this),': ',$this->a->value;
        }

}

// try to undestand why using a simple copy here would yield
// in an undesired result in the *-marked line
$a =&amp; new a(10);
$a->createRef();

$a->echoValue();
$a->b->echoValue();
$a->c->echoValue();

$a->value = 11;

$a->echoValue();
$a->b->echoValue(); // *
$a->c->echoValue();

/*
output:
class a: 10
class b: 10
class b: 10
class a: 11
class b: 11
class b: 11
*/
      </programlisting>
   </informalexample>
  </para>
</sect1>

 
 </chapter>
 
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