PHP namespace

Namespace is used to solve two types of problems encountered when creating reusable code such as classes or functions when writing class libraries or applications.

Name conflicts between user-written code and PHP internal classes/functions/constants or third-party classes/functions/constants.

Create an alias (or short) name for a very long identifier name (usually defined to alleviate the first type of problem), improving the readability of the source code.

1. Define the namespace

Use the namespace keyword to define the namespace, and use backslash "" as the separator.

For example:

namespace mytest;

namespace mytestspacex;

namespace mytest2spacexxxxx;

2. Use namespace

use MyFullClassname;

use MyFullClassname as Another, MyFullNSname;

3. PHP namespace dynamic characteristics

Variables or constants cannot be used after the use directive.

When calling a class, the class name and the namespace before the class name can be composed of variables.

namespace np1np2;

class Cls{

​​​ public static function test() {

​​​​                       print "test namespace 2n ";

}

}

namespace B;

np1np2Cls::test();

//np1np2Cls::test(); //Error, here is the call to Bnp1np2Cls::test()

$cls = "\np1\np2\Cls";

$cls::test();

$obj = new $cls();

$obj->test2();

4. Name resolution follows the following rules :

1. Calls to functions, classes and constants with fully qualified names are resolved at compile time. For example, new AB resolves to class AB.

2. All unqualified names and qualified names (non-fully qualified names) are converted at compile time according to the current import rules. For example, if namespace ABC was imported as C, then calls to CDe() would be converted to ABCDe().

3. Within the namespace, all qualified names that are not converted according to import rules will have the current namespace name in front of them. For example, if CDe() is called within namespace AB, CDe() will be converted to ABCDe().

4. Unqualified class names are converted at compile time according to the current import rules (full names are used instead of short import names). For example, if namespace ABC is imported as C, then new C() is converted to new ABC() .

5. Within a namespace (such as AB), function calls to unqualified names are resolved at runtime. For example, a call to function foo() is parsed like this:

1) Find a function named ABfoo() in the current namespace

2) Try to find and call function foo() in the global space.

6. Calls to unqualified names or qualified name classes (non-fully qualified names) within a namespace (such as AB) are resolved at runtime. The following is the parsing process of calling new C() and new DE(): Parsing of new C():

1) Find the ABC class in the current namespace.

2) Try to autoload class ABC.

Parsing of new DE():

1) Add the current namespace name in front of the class name to become: ABDE, and then search for the class.

2) Try to autoload class ABDE.

In order to reference a global class in the global namespace, the fully qualified name new C() must be used.