Global objects in php
INSIDE CODE and OUTSIDE CODE
class Item
/**
* This is INSIDE CODE because it is written INSIDE the class.
*/
public $label ;
public $price ;
>
/**
* This is OUTSIDE CODE because it is written OUTSIDE the class.
*/
$item = new Item ();
$item -> label = ‘Ink-Jet Tatoo Gun’ ;
$item -> price = 49.99 ;
?>
Ok, that’s simple enough. I got it inside and out. The big problem with this is that the Item class is COMPLETELY IGNORANT in the following ways:
* It REQUIRES OUTSIDE CODE to do all the work AND to know what and how to do it — huge mistake.
* OUTSIDE CODE can cast Item properties to any other PHP types (booleans, integers, floats, strings, arrays, and objects etc.) — another huge mistake.
Note: we did it correctly above, but what if someone made an array for $price? FYI: PHP has no clue what we mean by an Item, especially by the terms of our class definition above. To PHP, our Item is something with two properties (mutable in every way) and that’s it. As far as PHP is concerned, we can pack the entire set of Britannica Encyclopedias into the price slot. When that happens, we no longer have what we expect an Item to be.
INSIDE CODE should keep the integrity of the object. For example, our class definition should keep $label a string and $price a float — which means only strings can come IN and OUT of the class for label, and only floats can come IN and OUT of the class for price.
class Item
/**
* Here’s the new INSIDE CODE and the Rules to follow:
*
* 1. STOP ACCESS to properties via $item->label and $item->price,
* by using the protected keyword.
* 2. FORCE the use of public functions.
* 3. ONLY strings are allowed IN & OUT of this class for $label
* via the getLabel and setLabel functions.
* 4. ONLY floats are allowed IN & OUT of this class for $price
* via the getPrice and setPrice functions.
*/
protected $label = ‘Unknown Item’ ; // Rule 1 — protected.
protected $price = 0.0 ; // Rule 1 — protected.
public function getLabel () < // Rule 2 - public function.
return $this -> label ; // Rule 3 — string OUT for $label.
>
public function getPrice () < // Rule 2 - public function.
return $this -> price ; // Rule 4 — float OUT for $price.
>
public function setLabel ( $label ) // Rule 2 — public function.
/**
* Make sure $label is a PHP string that can be used in a SORTING
* alogorithm, NOT a boolean, number, array, or object that can’t
* properly sort — AND to make sure that the getLabel() function
* ALWAYS returns a genuine PHP string.
*
* Using a RegExp would improve this function, however, the main
* point is the one made above.
*/
if( is_string ( $label ))
$this -> label = (string) $label ; // Rule 3 — string IN for $label.
>
>
public function setPrice ( $price ) // Rule 2 — public function.
/**
* Make sure $price is a PHP float so that it can be used in a
* NUMERICAL CALCULATION. Do not accept boolean, string, array or
* some other object that can’t be included in a simple calculation.
* This will ensure that the getPrice() function ALWAYS returns an
* authentic, genuine, full-flavored PHP number and nothing but.
*
* Checking for positive values may improve this function,
* however, the main point is the one made above.
*/
if( is_numeric ( $price ))
$this -> price = (float) $price ; // Rule 4 — float IN for $price.
>
>
>
?>
Now there is nothing OUTSIDE CODE can do to obscure the INSIDES of an Item. In other words, every instance of Item will always look and behave like any other Item complete with a label and a price, AND you can group them together and they will interact without disruption. Even though there is room for improvement, the basics are there, and PHP will not hassle you. which means you can keep your hair!
If you have problems with overriding private methods in extended classes, read this:)
The manual says that «Private limits visibility only to the class that defines the item». That means extended children classes do not see the private methods of parent class and vice versa also.
As a result, parents and children can have different implementations of the «same» private methods, depending on where you call them (e.g. parent or child class instance). Why? Because private methods are visible only for the class that defines them and the child class does not see the parent’s private methods. If the child doesn’t see the parent’s private methods, the child can’t override them. Scopes are different. In other words — each class has a private set of private variables that no-one else has access to.
A sample demonstrating the percularities of private methods when extending classes:
abstract class base <
public function inherited () <
$this -> overridden ();
>
private function overridden () <
echo ‘base’ ;
>
>
class child extends base <
private function overridden () <
echo ‘child’ ;
>
>
$test = new child ();
$test -> inherited ();
?>
Output will be «base».
If you want the inherited methods to use overridden functionality in extended classes but public sounds too loose, use protected. That’s what it is for:)
A sample that works as intended:
abstract class base <
public function inherited () <
$this -> overridden ();
>
protected function overridden () <
echo ‘base’ ;
>
>
class child extends base <
protected function overridden () <
echo ‘child’ ;
>
>
$test = new child ();
$test -> inherited ();
?>
Output will be «child».
$GLOBALS
An associative array containing references to all variables which are currently defined in the global scope of the script. The variable names are the keys of the array.
Examples
Example #1 $GLOBALS example
function test () $foo = «local variable» ;
echo ‘$foo in global scope: ‘ . $GLOBALS [ «foo» ] . «\n» ;
echo ‘$foo in current scope: ‘ . $foo . «\n» ;
>
$foo = «Example content» ;
test ();
?>
The above example will output something similar to:
$foo in global scope: Example content $foo in current scope: local variable
As of PHP 8.1.0, write access to the entire $GLOBALS array is no longer supported:
Example #2 writing entire $GLOBALS will result in error.
// Generates compile-time error:
$GLOBALS = [];
$GLOBALS += [];
$GLOBALS =& $x ;
$x =& $GLOBALS ;
unset( $GLOBALS );
array_pop ( $GLOBALS );
// . and any other write/read-write operation on $GLOBALS
?>
Notes
Note:
This is a ‘superglobal’, or automatic global, variable. This simply means that it is available in all scopes throughout a script. There is no need to do global $variable; to access it within functions or methods.
Note: Variable availability
Unlike all of the other superglobals, $GLOBALS has essentially always been available in PHP.
Note:
As of PHP 8.1.0, $GLOBALS is now a read-only copy of the global symbol table. That is, global variables cannot be modified via its copy. Previously, $GLOBALS array is excluded from the usual by-value behavior of PHP arrays and global variables can be modified via its copy.
// Before PHP 8.1.0
$a = 1 ;
$globals = $GLOBALS ; // Ostensibly by-value copy
$globals [ ‘a’ ] = 2 ;
var_dump ( $a ); // int(2)
// As of PHP 8.1.0
// this no longer modifies $a. The previous behavior violated by-value semantics.
$globals = $GLOBALS ;
$globals [ ‘a’ ] = 1 ;
// To restore the previous behavior, iterate its copy and assign each property back to $GLOBALS.
foreach ( $globals as $key => $value ) $GLOBALS [ $key ] = $value ;
>
?>