我可以扩展php类型吗？

e.g.

class MyFloat extends float {
  function Formatted() {
    return number_format($this->value,2);
  }
}

and later use 123.Formatted?

I don't believe you can as float is a primitive not a class, but I could be wrong.

I am certain you can't do that, not on float at least.

You could make your own class though...

class MyFloat { 
   private $value;

   public function __construct($value) {
       if ( ! is_float($value)) {
           throw new Exception('Floats only');
       }
       $this->value = $value;
   } 

  public function formatted($places) {
       return number_format($this->value, $places);
  }

  public function get() {
      return $value;
  }
}

PHP just needs a __toInt() magic method :)

There is SplFloat for your extension pleasures. However, it is not yet available in current PHP versions. And it won't impact basic language semantics either way. It will always be a separate class. (PHP is what's commonly called an "unpure" OOP language.)

But for "future compatibility", you could choose this name for extension purposes.

if (!class_exists("SplFloat")) { class SplFloat {} }

class MyFloat extends SplFloat {
   ...