Instantiating a Namespaced PHP Class Dynamically

It’s pretty well known that you can instante a PHP class with a dynamic name using a variable:

$class = 'Foo_Bar';
$object = new $class();

is the same as

$object = new Foo_Bar();

It gets a little trickier if your class is defined in a namespace and you’re instantiating it from outside of that namespace. If you’re hard-coding a class, you need to use a leading backslash to reference the class.

namespace App;
$object = new \Foo\Bar();

// this would try to instantiate App\Foo\Bar
//$object = new Foo\Bar();

But if you’re using a dynamic name, the string should not have the leading backslash because the backslash is not part of the class name.

namespace App;
$class = 'Foo\Bar';
$object = new $class();

If you include the slash, your code won’t run on PHP 5.3.2 — you’ll get a Class '\\Foo\\Bar' not found error. This stackoverflow post set me straight. As mentioned in the post, the code will work in PHP >= 5.3.3 with or without the slash.

This tip was reposted from my blog, jontai.me