PHP中的对象内的heredoc变量

Question

The following php code will throw an error:

class Foo{
    public $bar = <<<EOF
         {$this->foobar}
EOF;
    public $foobar = "123";

   public function echoBar(){
         echo $this->bar;
   }
}

It doesn't even have to be in brackets, any attempt at variable substitution throws an error.

Can someone explain why? Putting the heredoc inside a function fixes the error, but I was wondering what causes this.

Version of php shell is Zend Engine v2.3.0.

Answer 1

The answer is here in the official PHP docs:

Heredocs can not be used for initializing class properties. Since PHP 5.3, this limitation is valid only for heredocs containing variables.