When would you use the $this keyword in PHP?
The most common use case is within Object Oriented Programming, while defining or working within a class. For example:
class Horse {
var $running = false;
function run() {
$this->running = true;
}
}
As you can see, within the run
function, we can use the $this
variable to refer to the instance of the Horse class that we are "in". So the other thing to keep in mind is that if you create 2 Horse classes, the $this
variable inside of each one will refer to that specific instance of the Horse class, not to them both.
A class may contain its own constants, variables (called "properties"), and functions (called "methods").
<?php
class SimpleClass
{
// property declaration
public $var = 'a default value';
// method declaration
public function displayVar() {
echo $this->var;
}
}
?>
Some examples of the $this pseudo-variable:
<?php
class A
{
function foo()
{
if (isset($this)) {
echo '$this is defined (';
echo get_class($this);
echo ")\n";
} else {
echo "\$this is not defined.\n";
}
}
}
class B
{
function bar()
{
// Note: the next line will issue a warning if E_STRICT is enabled.
A::foo();
}
}
$a = new A();
$a->foo();
// Note: the next line will issue a warning if E_STRICT is enabled.
A::foo();
$b = new B();
$b->bar();
// Note: the next line will issue a warning if E_STRICT is enabled.
B::bar();
?>
The above example will output:
- $this is defined (A)
- $this is not defined.
- $this is defined (B)
- $this is not defined.