Using namespaces: fallback to global function/constant

(PHP 5 >= 5.3.0, PHP 7, PHP 8)

Inside a namespace, when PHP encounters an unqualified Name in a class name, function or constant context, it resolves these with different priorities. Class names always resolve to the current namespace name. Thus to access internal or non-namespaced user classes, one must refer to them with their fully qualified Name as in:

Example #1 Accessing global classes inside a namespace

namespace A\B\C;
Exception extends \Exception {}

$a = new Exception('hi'); // $a is an object of class A\B\C\Exception
$b = new \Exception('hi'); // $b is an object of class Exception

$c = new ArrayObject; // fatal error, class A\B\C\ArrayObject not found

For functions and constants, PHP will fall back to global functions or constants if a namespaced function or constant does not exist.

Example #2 global functions/constants fallback inside a namespace

namespace A\B\C;

E_ERROR = 45;
return \
strlen($str) - 1;

E_ERROR, "\n"; // prints "45"
echo INI_ALL, "\n"; // prints "7" - falls back to global INI_ALL

echo strlen('hi'), "\n"; // prints "1"
if (is_array('hi')) { // prints "is not array"
echo "is array\n";
} else {
"is not array\n";

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User Contributed Notes 1 note

markus at malkusch dot de
8 years ago
You can use the fallback policy to provide mocks for built-in functions like time(). You therefore have to call those functions unqualified:

namespace foo;

time() {

assert (1234 == time());

However there's a restriction that you have to define the mock function before the first usage in the tested class method. This is documented in Bug #68541.

You can find the mock library php-mock at GitHub.
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