PHP Namespaces Referencing a class or function in a namespace
Example
As shown in Declaring Namespaces, we can define a class in a namespace as follows:
namespace MyProject\Shapes;
class Rectangle { ... }
To reference this class the full path (including the namespace) needs to be used:
$rectangle = new MyProject\Shapes\Rectangle();
This can be shortened by importing the class via the use-statement:
// Rectangle becomes an alias to MyProject\Shapes\Rectangle
use MyProject\Shapes\Rectangle;
$rectangle = new Rectangle();
As for PHP 7.0 you can group various use-statements in one single statement using brackets:
use MyProject\Shapes\{
Rectangle, //Same as `use MyProject\Shapes\Rectangle`
Circle, //Same as `use MyProject\Shapes\Circle`
Triangle, //Same as `use MyProject\Shapes\Triangle`
Polygon\FiveSides, //You can also import sub-namespaces
Polygon\SixSides //In a grouped `use`-statement
};
$rectangle = new Rectangle();
Sometimes two classes have the same name. This is not a problem if they are in a different namespace, but it could become a problem when attempting to import them with the use-statement:
use MyProject\Shapes\Oval;
use MyProject\Languages\Oval; // Apparantly Oval is also a language!
// Error!
This can be solved by defining a name for the alias yourself using the as keyword:
use MyProject\Shapes\Oval as OvalShape;
use MyProject\Languages\Oval as OvalLanguage;
To reference a class outside the current namespace, it has to be escaped with a \, otherwise a relative namespace path is assumed from the current namespace:
namespace MyProject\Shapes;
// References MyProject\Shapes\Rectangle. Correct!
$a = new Rectangle();
// References MyProject\Shapes\Rectangle. Correct, but unneeded!
$a = new \MyProject\Shapes\Rectangle();
// References MyProject\Shapes\MyProject\Shapes\Rectangle. Incorrect!
$a = new MyProject\Shapes\Rectangle();
// Referencing StdClass from within a namespace requires a \ prefix
// since it is not defined in a namespace, meaning it is global.
// References StdClass. Correct!
$a = new \StdClass();
// References MyProject\Shapes\StdClass. Incorrect!
$a = new StdClass();
