PHP手册-__NAMESPACE__关键字（命名空间中继承其他命名空间中类注意）

常量__ NAMESPACE__的值是包含当前命名空间名称的字符串。在全局的，不包括在任何命名空间中的代码，它包含一个空的字符串。

When extending a class from another namespace that should instantiate a class from within the current namespace, you need to pass on the namespace. <?php // File1.php namespace foo; class A {     public function factory() {         return new C;     } } class C {     public function tell() {         echo "foo";     } } ?> <?php // File2.php namespace bar; class B extends \foo\A {} class C {     public function tell() {         echo "bar";     } } ?> <?php include "File1.php"; include "File2.php"; $b = new bar\B; $c = $b->factory(); $c->tell(); // "foo" but you want "bar" ?> You need to do it like this: When extending a class from another namespace that should instantiate a class from within the current namespace, you need to pass on the namespace. <?php // File1.php namespace foo; class A {     protected $namespace = __NAMESPACE__;//此处是重点1，这样可以指定到当前命名空间中的对应类     public function factory() {         $c = $this->namespace . '\C';//此处是重点2，这样可以指定到当前命名空间中的对应类         return new $c;     } } class C {     public function tell() {         echo "foo";     } } ?> <?php // File2.php namespace bar; class B extends \foo\A {     protected $namespace = __NAMESPACE__; } class C {     public function tell() {         echo "bar";     } } ?> <?php include "File1.php"; include "File2.php"; $b = new bar\B; $c = $b->factory(); $c->tell(); // "bar" ?> (it seems that the namespace-backslashes are stripped from the source code in the preview, maybe it works in the main view. If not: fooA was written as \foo\A and barB as bar\B)