Defining class methods in PHP

Question

Is it possible in PHP (as it is in C++) to declare a class method OUTSIDE the class definition?

Answer 1

As PHP 5.3 supports closures, you can dynamically define instance methods as variables holding closures:

$class->foo = function (&$self, $n) {
  print "Current \$var: " . $self->var . "\n";
  $self->var += $n;
  print "New \$var:     " .$self->var . "\n";
};

Taking $self (you can't use $this outside object context) as a reference (&), you can modify the instance.

However, problems occur when you try to call the function normally:

$class->foo(2);

You get a fatal error. PHP thinks foo is a method of $class, because of the syntax. Also, you must pass the instance as the first argument.

There is luckily a special function for calling functions by name called call_user_func:

call_user_func($class->foo, &$class, 2);
# => Current $var: 0
# => New $var:     2

Just remember to put & before the instance variable.

What's even easier is if you use the __call magic method:

class MyClass {
  public function __call ($method, $arguments)  {
    if (isset($this->$method)) {
      call_user_func_array($this->$method, array_merge(array(&$this), $arguments));
    }
  }
}

Now you can call $class->foo(2) instead. The magic __call method catches the call to an unknown method, and calls the closure in the $class->foo variable with the same name as the called method.

Of course, if $class->var was private, the closure in stored in the $class->foo variable wouldn't be able to access it.