Posted by Stas on August 17, 2007
Q. Why PHP needs namespaces?
A. Because long names like PEAR_Form_Loader_Validate_Table_Element_Validator_Exception are really tiresome.
Q. What is the main goal of the namespace implementation?
A. To solve the problem above.
Q. What “namespace X::Y::Z” means?
A: 1. All class/function/method names are prefixed with X::Y::Z.
2. All class/function/method names are resolved first against X::Y::Z.
Q. What “import X::Y::Z as Foo” means?
A. Every time there’s Foo as a class/function name or prefix to the name, it really means X::Y::Z
Q. What “import X::Y::Z” means?
A. “import X::Y::Z as Z”, then see above.
Q. What “import Foo” means?
Q. What is the scope of namespace and import?
A. Current file.
Q. Can same namespace be used in multiple files?
Q. Is there any relation between namespaces X::Y::Z and X::Y?
A. Only in programmer’s mind.
Q. How do I import all classes from namespace X::Y::Z into global space?
A. You don’t, since it brings back the global space pollution problem.
Instead, you import X::Y::Z and then prefix your classes with Z::.
Q. But doesn’t it mean I will still have long names?
A. Not longer then three elements: Namespace::Class::Element.
Q. Why it is not implemented like in <insert your favorite language here>?
A. Because PHP is not <insert your favorite language here> ;)
Also we are considering to add one more feature to namespaces – ability to declare a namespaced constant – i.e. constant named Name::Space::NAME – with same resolution rules like classes – with const operator. Consequently it may be also possible to have const NAME = ‘value’ in global context, meaning the same as define(‘NAME’, ‘value’).
Also note namespaces are still work in progress, so it may happen it would be changed a lot when it’s released.