PHP Declare Statement
Description
In PHP declare construct is used to set execution directives for a block of code. At present two directives are recognized ticks and encoding.
Syntax:
declare (directive) statement
The following table describes two directives currently supported.
Directive | Description |
---|---|
ticks | A tick is an event. While the format of specifying the tick directive is tick=N, where N is an integer. The tick event occurs for every N statements (following the declare). Usually, condition expressions and argument expressions are excluded from being executed. Register_tick_function() is used to specify each event(s) that occur on each tick. Remember that this directive is deprecated in PHP5.3. |
encoding | The encoding directive specifies a script's encoding. Usage of this detective is decal re(encoding="EncodingType") where EncodingType is a encoding type like ISO-8859-1. This directive can be used only if PHP is compiled with --enable-zend-multibyte. You can use phpinfo() to know whether a PHP installation |
Example of PHP declare statement using tick directive
<?php
declare(ticks=5);
// the following function is called on each tick event
function w3r_tick()
{
echo "w3r_tick() called<br>";
}
register_tick_function('w3r_tick');
$a = 5;
if ($a > 0)
{
$a += 2;
print($a);
}
?>
View the example in the browser
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PHP: Tips of the Day
Members of objects or classes can be accessed using the object operator (->) and the class operator (::).
Example:
class MyClass { public $a = 1; public static $b = 2; const C = 3; public function d() { return 4; } public static function e() { return 5; } } $object = new MyClass(); var_dump($object->a); // int(1) var_dump($object::$b); // int(2) var_dump($object::C); // int(3) var_dump(MyClass::$b); // int(2) var_dump(MyClass::C); // int(3) var_dump($object->d()); // int(4) var_dump($object::d()); // int(4) var_dump(MyClass::e()); // int(5) $classname = "MyClass"; var_dump($classname::e()); // also works! int(5)
Note that after the object operator, the $ should not be written ($object->a instead of $object->$a). For the class operator, this is not the case and the $ is necessary. For a constant defined in the class, the $ is never used.
Also note that var_dump(MyClass::d()); is only allowed if the function d() does not reference the object:
class MyClass { private $a = 1; public function d() { return $this->a; } } $object = new MyClass(); var_dump(MyClass::d()); // Error!
This causes a 'PHP Fatal error: Uncaught Error: Using $this when not in object context'
These operators have left associativity, which can be used for 'chaining':
class MyClass { private $a = 1; public function add(int $a) { $this->a += $a; return $this; } public function get() { return $this->a; } } $object = new MyClass(); var_dump($object->add(4)->get()); // int(5)
These operators have the highest precedence (they are not even mentioned in the manual), even higher that clone. Thus:
class MyClass { private $a = 0; public function add(int $a) { $this->a += $a; return $this; } public function get() { return $this->a; } } $o1 = new MyClass(); $o2 = clone $o1->add(2); var_dump($o1->get()); // int(2) var_dump($o2->get()); // int(2)
The value of $o1 is added to before the object is cloned!
Note that using parentheses to influence precedence did not work in PHP version 5 and older (it does in PHP 7):
// using the class MyClass from the previous code $o1 = new MyClass(); $o2 = (clone $o1)->add(2); // Error in PHP 5 and before, fine in PHP 7 var_dump($o1->get()); // int(0) in PHP 7 var_dump($o2->get()); // int(2) in PHP 7
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