caller.hh

<?hh // strict

class Caller {
  public function set(string $property_name, Foo $object): void {
    $object->$property_name = 'poopy';
  }
  public function call(string $property_name, Foo $object): string {
  	return $object->$property_name;
  }
}

foo.hh

?hh // strict

class Foo {

}

main.php

<?php
require 'foo.hh';
require 'caller.hh';

$caller = new Caller();
$foo = new Foo();

$caller->set('poo', $foo);

echo $caller->call('poo', $foo);

output.txt

$ hh_client .
/home/vagrant/dynamic_properties/caller.hh:5:14,27: Dynamic method call (Naming[2011])
/home/vagrant/dynamic_properties/caller.hh:8:20,33: Dynamic method call (Naming[2011])
$ hhvm main.php
poopy