是否可以在类范围中定义匿名函数？

Question

I'd like to assign anonymous functions to arrays in PHP inside of a class, but I keep stumbling over syntax errors.

class Stuff {
  private $_preference_defaults = array(
    'cookie'    => true,
    'session'   => true,
    'database'  => true,
    'filter'    => function($input) { return true; },
    'sanitizer' => function($input) { return $input; },
  );
};

Will throw an unexpected T_FUNCTION syntax error, and it doesn't matter whether or not the array is static. I got desperate and tried the "old" way of doing it:

class Stuff {
  private $_preference_defaults = array(
    'cookie'    => true,
    'session'   => true,
    'database'  => true,
    'filter'    => create_function('$input', 'return true;'),
    'sanitizer' => create_function('$input', 'return $input;'),
  );
};

And this led to an unexpected '(', expecting ')' syntax error. However, if I define the functions ahead of time, it does work:

class Stuff {
  function _preference_default_filter($input) {
    return true;
  }
  function _preference_default_sanitizer($input) {
    return true;
  }
  private $_preference_defaults = array(
    'cookie'    => true,
    'session'   => true,
    'database'  => true,
    'filter'    => _preference_default_filter,
    'sanitizer' => _preference_default_sanitizer,
  );
};

And then I'm able to call those functions within a class method:

function do_stuff($foo) {
  return $this->{$this->_preference_defaults['filter']}($foo);
}

Not only is this syntactically sour, in my head it wreaks of poor style and I can imagine this sort of trickery causing headaches in the future.

1. Am I not able to create an anonymous function at class (static) scope? (I'm thinking maybe because a valid Closure object cannot be created in that context?)
2. Is there a more... PHP... means to the same end? That is to say, is there a "better" way of assigning trivial default callbacks to array values in class scope? The final snippet I provided gets the job done for sure, but I'd prefer a solution that won't leave me asking the optometrist for a stronger prescription.

Answer 1

Am I not able to create an anonymous function at class (static) scope? (I'm thinking maybe because a valid Closure object cannot be created in that context?)

Yes, because the initial values of class attributes should be known in parsing step, while function call and anonymous function require runtime

Also see here to get the additional details: https://stackoverflow.com/a/9029556/251311

And cannot get your second question :-S