将来作为面试PHP的题目

$instance = new SimpleClass();

$assigned   =  $instance;
$reference  =& $instance;

$instance->var = '$assigned will have this value';

$instance = null; // $instance and $reference become null

var_dump($instance);
var_dump($reference);
var_dump($assigned);

　　

<?php $a = 'car'; // $a is a string $a[0] = 'b'; // $a is still a string echo $a; // bar ?>

　　

$var1 = "Example variable";
$var2 = "";

function global_references($use_globals)
{
    global $var1, $var2;
    if (!$use_globals) {
        $var2 =& $var1; // visible only inside the function
    } else {
        $GLOBALS["var2"] =& $var1; // visible also in global context
    }
}

global_references(false);
echo "var2 is set to '$var2'\n"; // var2 is set to ''
global_references(true);
echo "var2 is set to '$var2'\n"; // var2 is set to 'Example variable'

　　把 global $var; 当成是 $var =& $GLOBALS['var']; 的简写。从而将其它引用赋给 $var 只改变了本地变量的引用。