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Making the properties of a class available in the global scope - PHP

If you ever have the chance to gather a group of PHP programmers in a big room and ask them whether they find it hard to build classes with PHP, the invariable answer would probably be a resounding "No!" And admittedly, they’d be absolutely right, since PHP allows you to work with classes, methods, and properties in a pretty straightforward way. But there's more to programming with classes, as this article series will explain.

TABLE OF CONTENTS:
  1. Protecting PHP 5 Class Data with Member Visibility
  2. Making the properties of a class available in the global scope
  3. Restricting the access to class properties
  4. Accessing protected properties using class accessors
By: Alejandro Gervasio
Rating: starstarstarstarstar / 11
May 21, 2008

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In order to explain how to work with the member visibility feature in PHP 5, I’m going to start building a basic class that will be tasked with saving an inputted string of data to a specified text file. The complete signature of this sample class is listed below, so take the time to examine it, please:


// define 'DataSaver' class (saves a string of data to a target file and their properties are defined public)


class DataSaver{

public $filePath;

public $data;

public function __construct($data,$filePath){

if(!$data||strlen($data)>1024){

throw new Exception('Invalid data for being saved to target file.');

}

if(!file_exists($filePath)){

throw new Exception('Invalid target file.');

}

$this->data=$data;

$this->filePath=$filePath;

}

// save data to target file

public function save(){

if(!$fp=fopen($this->filePath,'w')){

throw new Exception('Error opening target file.');

}

if(!fwrite($fp,$this->data)){

throw new Exception('Error writing data to target file.');

}

fclose($fp);

}

// get target file via an accessor

public function getFilePath(){

return $this->filePath;

}

// get data via an accessor

public function getData(){

return $this->data;

}

}


The above “DataSaver” class isn’t going to change your life as a PHP developer, but it does demonstrate how to declare its two properties, called "$data” and “$filePath” as public members. This means that they can be freely accessed in the global scope.

However, to clarify this concept, in the next few lines, I've coded a simple script that first uses the previous class to save a trivial string to a determined text file, and then prints the pertinent values of the aforementioned properties on screen.

The corresponding code sample looks like this:


try{

// create new instance of 'DataSaver' class

$dataSaver=new DataSaver('This string of data will be saved to a target file!','datafile.txt');

// save data to target file

$dataSaver->save();

// print value of public properties

echo 'Target file is the following : '.$dataSaver->filePath.'<br />';

echo 'Data for being saved to target file is the following : '.$dataSaver->data;

 

/* displays the following

Target file is the following : datafile.txt

Data for being saved to target file is the following : This string of data will be saved to a target file!

*/

}

catch(Exception $e){

echo $e->getMessage();

exit();

}


Since the pair of class properties have been declared public using the “public” keyword, they can be accessed directly from outside the originating class, as illustrated clearly by the previous hands-on example. In this particular case, the values assigned to these basic properties are echoed to the browser without any kind of restrictions because they’re available in the global scope. Are you starting to grasp how to declare a couple of public properties within a PHP 5 class? I guess you are!

All right, now that you understand how to work with properties of class that have been declared public, it’s time to see how to switch their visibility to “protected.” This implies that they can’t be accessed in the global scope. They are only visible from inside the originating class and also from all their eventual subclasses.

But actually, I’m getting ahead of myself, since this topic will be discussed in detail in the following section. Therefore, click on the link below and keep reading.



 
 
>>> More PHP Articles          >>> More By Alejandro Gervasio
 

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