当我在Zend
PHP认证考试指南5.5中阅读OOP章时,我发现一个问题让我感到震惊.这个问题是：
class Magic
{
public $a = "A";
protected $b = array( "a" => "A","b" => "B","c" => "C" );
protected $c = array( 1,2,3 );
public function __get( $v )
{
echo "$v";
return $this->b[$v];
}
public function __set( $var,$val )
{
echo "$var: $val,";
$this->$var = $val;
}
}
$m = new Magic();
echo $m->a . "," . $m->b . "," . $m->c . ",";
$m->c = "CC";
echo $m->a . ",";
b,c,A,B,C,c: CC,b,C
为什么这个代码不能打印出来,它是如何工作的？
__get仅针对不存在或不可见的属性进行调用.换句话说,当你写
原文链接：https://www.f2er.com/php/138165.html$obj->prop
如果prop被定义并且在当前上下文中可见,则它将按原样返回,而不调用__get.
例：
class X {
public $pub = 1;
private $pri = 2;
function __get($v) {
echo "[get $v]\n";
return 42;
}
function test() {
echo $this->foo,"\n"; // __get invoked
echo $this->pri,"\n"; // no __get
echo $this->pub,"\n"; // no __get
}
}
$x = new X;
$x->test();
echo $x->foo,"\n"; // __get invoked
echo $x->pri,"\n"; // __get invoked (property not visible)
echo $x->pub,"\n"; // no __get
这就解释了为什么magic-> a不调用吸气剂.现在,由于你也定义了setter,所以magic-> c = CC实际上改变了类的受保护成员,因此,当你稍后回覆magic-> c时,这仍然调用getter(由于c的隐形),而getter返回这个> b [c],而不是这个> c的实际值.
以下是您的代码,为了清楚起见,稍作改写：
class Magic
{
public $a = "publicA";
protected $values = array( "a" => "valA","b" => "valB","c" => "valC" );
protected $c = "oldC";
public function __get( $v )
{
echo "[get $v]\n";
return $this->values[$v];
}
public function __set( $var,$val )
{
echo "[set $var=$val]\n";
$this->$var = $val;
}
}
$m = new Magic();
echo $m->a . "," . $m->c . "\n";
$m->c = "newC";
echo $m->a . "," . $m->c . "\n";
结果：
[get b] [get c] publicA,valB,valC # no getter for `a` [set c=newC] [get b] [get c] # getter still invoked for `c` publicA,valC # no getter for `a`
给读者一个练习：
如果您更换点,为什么输出不同.在echo语句中用逗号分隔：
$m = new Magic(); echo $m->a,",$m->b,$m->c,"\n"; $m->c = "newC"; echo $m->a . ","\n";
