PHP引用()使用详解(2)

如：$b=new a，其中new a产生的是一个匿名的a对象实例，而此时的$b是对这个匿名对象的拷贝。同理$c=$b，也是对$b内容的一个拷贝。所以在php4中，为了节省内存空间，$b=new a 一般会改成引用的模式，即 $b=& new a。

下面再来个 官方 提供的例子：

在php5中，你不需要额外添加什么东西就可到达“对象引用”的功能：

<?php
class foo{
        protected $name;
        function __construct($str){
                $this->name = $str;
        }
        function __toString(){
                return  'my name is "'. $this->name .'" and I live in "' . __CLASS__ . '".' . "\n";
        }
        function setName($str){
                $this->name = $str;
        }
}

class MasterOne{
        protected $foo;
        function __construct($f){
                $this->foo = $f;
        }
        function __toString(){
                return 'Master: ' . __CLASS__ . ' | foo: ' . $this->foo . "\n";
        }
        function setFooName($str){
                $this->foo->setName( $str );
        }
}

class MasterTwo{
        protected $foo;
        function __construct($f){
                $this->foo = $f;
        }
        function __toString(){
                return 'Master: ' . __CLASS__ . ' | foo: ' . $this->foo . "\n";
        }
        function setFooName($str){
                $this->foo->setName( $str );
        }
}

$bar = new foo('bar');

print("\n");
print("Only Created \$bar and printing \$bar\n");
print( $bar );

print("\n");
print("Now \$baz is referenced to \$bar and printing \$bar and \$baz\n");
$baz =& $bar;
print( $bar );

print("\n");
print("Now Creating MasterOne and Two and passing \$bar to both constructors\n");
$m1 = new MasterOne( $bar );
$m2 = new MasterTwo( $bar );
print( $m1 );
print( $m2 );

print("\n");
print("Now changing value of \$bar and printing \$bar and \$baz\n");
$bar->setName('baz');
print( $bar );
print( $baz );

print("\n");
print("Now printing again MasterOne and Two\n");
print( $m1 );
print( $m2 );

print("\n");
print("Now changing MasterTwo's foo name and printing again MasterOne and Two\n");
$m2->setFooName( 'MasterTwo\'s Foo' );
print( $m1 );
print( $m2 );

print("Also printing \$bar and \$baz\n");
print( $bar );
print( $baz );
?>

输出：

Only Created $bar and printing $bar
my name is "bar" and I live in "foo".

Now $baz is referenced to $bar and printing $bar and $baz
my name is "bar" and I live in "foo".

Now Creating MasterOne and Two and passing $bar to both constructors
Master: MasterOne | foo: my name is "bar" and I live in "foo".

Master: MasterTwo | foo: my name is "bar" and I live in "foo".

Now changing value of $bar and printing $bar and $baz
my name is "baz" and I live in "foo".
my name is "baz" and I live in "foo".

Now printing again MasterOne and Two
Master: MasterOne | foo: my name is "baz" and I live in "foo".

Master: MasterTwo | foo: my name is "baz" and I live in "foo".

Now changing MasterTwo's foo name and printing again MasterOne and Two
Master: MasterOne | foo: my name is "MasterTwo's Foo" and I live in "foo".

Master: MasterTwo | foo: my name is "MasterTwo's Foo" and I live in "foo".

Also printing $bar and $baz
my name is "MasterTwo's Foo" and I live in "foo".
my name is "MasterTwo's Foo" and I live in "foo".

上个例子解析：

$bar = new foo('bar');
$m1 = new MasterOne( $bar );
$m2 = new MasterTwo( $bar );