在php文件中重新定义类，现在生成一个函数

There is a file myclass.php:

<?php
class Myclass {
    public static function Fun1() {

    }
}

and i try to make an own framework where to use a code generation:

$class = "MyClass";
$function = "Fun1";
$fname = "myclass.php"
if (class_exists($class) && !method_exists($class, $functionName)) {
    $current = file_get_contents($fname);
    if ($current) {
        $strIndex = strlen($current);
        while ($strIndex-- && $current[$strIndex] != "}");//removing the last '}'
        $current = substr($current, 0, $strIndex);
        $current .= "\tpublic static function $functionName() {
";//there inserting the new function
        $current .= "
";
        $current .= "\t}
";
        $current .= "}
";
        $current .= "
";
        file_put_contents($fname, $current);
        require $fname;//I load the file again, but how to redeclare the class?
    }
}

.. and i get a message: Fatal error: Cannot redeclare class MyClass in C:\xampp\htdocs\myproj\index.php on line 12. Thank you.

"Extend" Myclass

class MyMyClass extends MyClass
{
    public function SomeNewMethod() {
    }
}