Simplify unsetting entity class properties

As far as I know the most IDE's unfortunately don't support the @property annotation introduced in phpDoc years ago.
So for good DX I don't think we can't get fully rid of the properties. :|

get_class_vars(get_class($this)); could be a solution, but as fago said we've to be careful because of the scope we use this. A helper function outside the class could work but seems a bit ugly.
If it is always true that properties that can be unset have a return from $this->getPropertyDefinition($property) we could use this as condition for unset properties returned by get_class_vars(get_class($this));. I think the patch I've posted in #1818556: Convert nodes to the new Entity Field API already uses this construct.

Reflection sounds interesting, but definitely would need a benchmark ;)

I've just figured out that, call_user_func('get_class_vars', get_class($this)) resets the scope the function is called in. That way we should be able to fetch just the public properties of a class within a method of the class itself.

I did some benchmarks to compare using plain unset() with dynamic approaches.
It looks like a generic approach takes up to 3 times longer - but it heavily depends on the number of the calls.
In absolute numbers this means for 100000 calls that the fastest dynamic approach takes 0.4842 seconds longer (260%) than the usage of unset().
The question now is, if this gain of DX is worth this :)

Used code:

class A {
  public $foo = 'foo';
  public $foobar = 'foo';
  public $one = 'one';
  public $two = 'two';
  protected $bar = 'bar';

  public function foo() {
    foreach (call_user_func('get_object_vars', $this) as $var) {
      unset($this->{$var});
    }
  }

  public function bar() {
    $closure = function($instance) { return get_object_vars($instance); };
    foreach ($closure($this) as $var) {
      unset($this->{$var});
    }
  }

  public function foobar() {
    foreach (foobar($this) as $var) {
      unset($this->{$var});
    }
  }

  public function reference() {
    unset(
      $this->foo,
      $this->foobar,
      $this->one,
      $this->two
    );
  }
}
function foobar($instance) {
  return get_object_vars($instance);
}

foreach (array(100, 1000, 10000, 100000) as $repeats) {
  echo str_repeat('-', 10) . ' Repeats ' . $repeats . ' ' . str_repeat('-', 10) . '<br>';
  $results = array();
  $A = new A();
  $time = microtime (TRUE);
  for($i=0; $i < $repeats; $i++) {
    $A->foo();
  }
  $key = '<span style="color:#A5700D;">foo</span>';
  $results[$key] = microtime (TRUE) - $time;
  echo $key . ': ' . round($results[$key], 6) . ' Sec<br>';

  $A = new A();
  $time = microtime (TRUE);
  for($i=0; $i < $repeats; $i++) {
    $A->bar();
  }
  $key = '<span style="color:#780BB7;">bar</span>';
  $results[$key] = microtime (TRUE) - $time;
  echo $key . ': ' . round($results[$key], 6) . ' Sec<br>';

  $A = new A();
  $time = microtime (TRUE);
  for($i=0; $i < $repeats; $i++) {
    $A->foobar();
  }
  $key = '<span style="color:#872923;">foobar</span>';
  $results[$key] = microtime (TRUE) - $time;
  echo $key . ': ' . round($results[$key], 6) . ' Sec<br>';

  $A = new A();
  $time = microtime (TRUE);
  for($i=0; $i < $repeats; $i++) {
    $A->reference();
  }
  $reference = microtime (TRUE) - $time;
  $reference_name = '<span style="color:#105E2A;">Reference</span>';
  echo $reference_name . ': ' . round($reference, 6) . ' Sec<br><br>';

  $winner = min($results);
  $winner_name = array_search($winner, $results);
  unset($results[$winner_name]);
  echo $winner_name . ' wins by ' . (round((min($results) / $winner) * 100, 6) - 100) . '%<br>';
  echo (($winner < $reference) ? $winner_name . ' beats ' . $reference_name . ' by ' : $reference_name . ' beats ' . $winner_name . ' by ') . round(($winner / $reference) * 100, 6) . '% [' . round(abs($reference - $winner), 5) . ' Sec]<br><br>';
}

Closing as duplicate of #2095919: Kill ContentEntityBase::init() , we don't need them anymore as we have interfaces & methods now, just need to get rid of the remaining ones :)