Name resolution rules
(PHP 5 >= 5.3.0, PHP 7)
For the purposes of these resolution rules, here are some important definitions:
Namespace name definitions Unqualified name
This is an identifier without a namespace separator, such as Foo
Qualified name
This is an identifier with a namespace separator, such as Foo\Bar
Fully qualified name
This is an identifier with a namespace separator that begins with a namespace separator, such as \Foo\Bar. The namespace \Foo is also a fully qualified name.
Relative name
This is an identifier starting with namespace, such as namespace\Foo\Bar.
Names are resolved following these resolution rules:
- Fully qualified names always resolve to the name without leading namespace separator. For instance \A\B resolves to A\B.
- Relative names always resolve to the name with namespace replaced by the current namespace. If the name occurs in the global namespace, the namespace_ prefix is stripped. For example _namespace\A inside namespace X\Y resolves to X\Y\A. The same name inside the global namespace resolves to A.
- For qualified names the first segment of the name is translated according to the current class/namespace import table. For example, if the namespace A\B\C is imported as C, the name C\D\E is translated to A\B\C\D\E.
- For qualified names, if no import rule applies, the current namespace is prepended to the name. For example, the name C\D\E inside namespace A\B, resolves to A\B\C\D\E.
- For unqualified names, the name is translated according to the current import table for the respective symbol type. This means that class-like names are translated according to the class/namespace import table, function names according to the function import table and constants according to the constant import table. For example, after use A\B\C; a usage such as new C() resolves to the name A\B\C(). Similarly, after use function A\B\fn; a usage such as fn() resolves to the name A\B\fn.
- For unqualified names, if no import rule applies and the name refers to a class-like symbol, the current namespace is prepended. For example new C() inside namespace A\B resolves to name A\B\C.
- For unqualified names, if no import rule applies and the name refers to a function or constant and the code is outside the global namespace, the name is resolved at runtime. Assuming the code is in namespace A\B, here is how a call to function foo() is resolved:
- It looks for a function from the current namespace: A\B\foo().
- It tries to find and call the global function foo().
Example #1 Name resolutions illustrated
<?php
namespace A;
use B\D, C\E as F;
// function calls
foo(); // first tries to call "foo" defined in namespace "A"
// then calls global function "foo"
\foo(); // calls function "foo" defined in global scope
my\foo(); // calls function "foo" defined in namespace "A\my"
F(); // first tries to call "F" defined in namespace "A"
// then calls global function "F"
// class references
new B(); // creates object of class "B" defined in namespace "A"
// if not found, it tries to autoload class "A\B"
new D(); // using import rules, creates object of class "D" defined in namespace "B"
// if not found, it tries to autoload class "B\D"
new F(); // using import rules, creates object of class "E" defined in namespace "C"
// if not found, it tries to autoload class "C\E"
new \B(); // creates object of class "B" defined in global scope
// if not found, it tries to autoload class "B"
new \D(); // creates object of class "D" defined in global scope
// if not found, it tries to autoload class "D"
new \F(); // creates object of class "F" defined in global scope
// if not found, it tries to autoload class "F"
// static methods/namespace functions from another namespace
B\foo(); // calls function "foo" from namespace "A\B"
B::foo(); // calls method "foo" of class "B" defined in namespace "A"
// if class "A\B" not found, it tries to autoload class "A\B"
D::foo(); // using import rules, calls method "foo" of class "D" defined in namespace "B"
// if class "B\D" not found, it tries to autoload class "B\D"
\B\foo(); // calls function "foo" from namespace "B"
\B::foo(); // calls method "foo" of class "B" from global scope
// if class "B" not found, it tries to autoload class "B"
// static methods/namespace functions of current namespace
A\B::foo(); // calls method "foo" of class "B" from namespace "A\A"
// if class "A\A\B" not found, it tries to autoload class "A\A\B"
\A\B::foo(); // calls method "foo" of class "B" from namespace "A"
// if class "A\B" not found, it tries to autoload class "A\B"
?>← Using namespaces: fallback to global function/constant
FAQ: things you need to know about namespaces →
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