<?php

class Person {
  public $name;

  public function wave()
  {
    return $this->name. ' is waving';
  }

  public function waveAt(Person $waveTarget)
  {
    return $this->name . ' waves at ' . $waveTarget->name;
  }
}

$boo = new Person();
$boo->name = 'Boo';
var_dump($boo->wave());

$hay = new Person();
$hay->name = 'Hay';
var_dump($hay->wave());

var_dump($boo->waveAt($hay));