在PHP中,出現同名函數或是同名類是不被允許的。爲防止編程人員在項目中定義的類名或函數名出現重複衝突,在PHP5.3中引入了命名空間這一概念。
1.命名空間,即將代碼劃分成不同空間,不同空間的類名相互獨立,互不衝突。一個php文件中可以存在多個命名空間,第一個命名空間前不能有任何代碼。內容空間聲明後的代碼便屬於這個命名空間,例如:
<?php
echo 111; //由於namespace前有代碼而報錯
namespace Teacher;
class Person{
function __construct(){
echo 'Please study!';
}
}
2.調用不同空間內類或方法需寫明命名空間。例如:
<?php
namespace Teacher;
class Person{
function __construct(){
echo 'Please study!<br/>';
}
}
function Person(){
return 'You must stay here!';
};
namespace Student;
class Person{
function __construct(){
echo 'I want to play!<br/>';
}
}
new Person(); //本空間(Student空間)
new \Teacher\Person(); //Teacher空間
new \Student\Person(); //Student空間
echo \Teacher\Person(); //Teacher空間下Person函數
//輸出:
I want to play!
Please study!
I want to play!
You must stay here!
3.在命名空間內引入其他文件不會屬於本命名空間,而屬於公共空間或是文件中本身定義的命名空間。例:
首先定義一個1.php和2.php文件:
<?php //1.php
class Person{
function __construct(){
echo 'I am one!<br/>';
}
}
<?php
namespace Newer;
require_once './1.php';
new Person(); //報錯,找不到Person;
new \Person(); //輸出 I am tow!;
<?php //2.php
namespace Two
class Person{
function __construct(){
echo 'I am tow!<br/>';
}
}
<?php
namespace New;
require_once './2.php';
new Person(); //報錯,(當前空間)找不到Person;
new \Person(); //報錯,(公共空間)找不到Person;
new \Two\Person(); //輸出 I am tow!;
4.下面我們來看use的使用方法:(use以後引用可簡寫)
namespace School\Parents;
class Man{
function __construct(){
echo 'Listen to teachers!<br/>';
}
}
namespace School\Teacher;
class Person{
function __construct(){
echo 'Please study!<br/>';
}
}
namespace School\Student;
class Person{
function __construct(){
echo 'I want to play!<br/>';
}
}
new Person(); //輸出I want to play!
new \School\Teacher\Person(); //輸出Please study!
new Teacher\Person(); //報錯
----------
use School\Teacher;
new Teacher\Person(); //輸出Please study!
----------
use School\Teacher as Tc;
new Tc\Person(); //輸出Please study!
----------
use \School\Teacher\Person;
new Person(); //報錯
----------
use \School\Parent\Man;
new Man(); //報錯