Getting Started with Objects with PHP V5

class Dictionary {

    public $translations = array();

    public $type ="En";

}

As you can see, you can declare a property and assign its value at the same time. You can get a quick peek at the state of an object with the print_r() function. Listing 2 shows that a Dictionary object now has more to it.

$en = new Dictionary();

print_r( $en );  



If we run this script, we'll see output of:



Dictionary Object

(

    [translations] => Array

        (

        )



    [type] => En

)

You can access public object properties using the object operator '->'. So $en->type means the $type property of the Dictionary object referenced by $en. If you can access a property, it means that you can set and get its value. The code in Listing 3 creates two instances of the Dictionary class -- in other words, it instantiates two Dictionary objects. It changes the $type property of one object and adds translations to both:

$en = new Dictionary();

$en->translations['TREE'] = "tree";



$fr = new Dictionary();

$fr->type = "Fr";

$fr->translations['TREE'] = "arbre";



foreach ( array( $en, $fr ) as $dict ) {

    print "type: {$dict->type} ";

    print "TREE: {$dict->translations['TREE']}\n";

}

The script outputs the following:

type: En TREE: tree

type: Fr TREE: arbre

So the Dictionary class is now a little more useful. Individual objects can store distinct sets of keys and values, as well as a flag that tells a client more about the kind of Dictionary this is.

Even though the Dictionary class is currently little more than a wrapper around an associative array, there is some clue to the power of objects here. At this stage, we could represent our sample data pretty well, as shown in Listing 4.

$en = array(

    'translations'=>array( 'TREE' => 'tree' ),

    'type'=>'En'

);



$fr = array(

    'translations'=>array( 'TREE' => 'arbre' ),

    'type'=>'Fr'

);

Although this data structure fulfills the same purpose as the Dictionary class, it provides no guarantee of the structure. If you are passed a Dictionary object, you know it is designed to have a $translations property. Given an associative array, you have no such guarantee. This fact makes a query like $fr['translations']['TREE']; somewhat hit and miss, unless the code making the query is sure of the provenance of the array. This is a key point about objects: The type of an object is a guarantee of its characteristics.

Although there are benefits to storing data with objects, you are missing an entire dimension. Objects can be things, but crucially they can also do things.

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