PHP and MySQL Web Development 4th Ed-tqw-_darksiderg

Understanding Advanced Object-Oriented Functionality in PHP
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Additionally, you can use class type hinting. Normally, when you pass a parameter to a
function in PHP, you do not pass the type of that parameter.With class type hinting, you
can specify the type of class that ought to be passed in, and if that is not the type actually
passed in, an error will be triggered.The type checking is equivalent to instanceof.For
example, consider the following function:
function check_hint(B $someclass)
{
//...
}
This example suggests that $someclass needs to be an instance of class B. If you then
pass in an instance of class A as
check_hint($a);
you will get the following fatal error:
Fatal error: Argument 1 must be an instance of B
Note that if you had hinted A and passed in an instance of B, no error would have
occurred because B inherits from A.
Late Static Bindings
Introduced in PHP 5.3, late static bindings allow references to the called class within the
context of a static inheritance; parent classes can use static methods overridden by child
classes. The following basic example from the PHP Manual shows a late static binding
in action:
The above example will output:
B
Allowing references to classes called at runtime, regardless if they have been overridden,
brings additional object functionality to your classes.