คือผมสงสัยมากถึงมากที่สุดว่า OOP ดีกว่า Function ธรรมดายังไง ? - -"

<?php 

class TemperatureDegrees{
	private $value;
	private $temperatureUnit;
	
	public function __construct($value,$temperatureUnit){
		$this->value=$value;
		$this->temperatureUnit=$temperatureUnit;
		$temperatureUnit->setTemperatureDegrees($this);
	}
	
	public function setTemperatureUnit($temperatureUnit){
		$this->temperatureUnit=$temperatureUnit;
	}
	
	public function getValue(){
		return ($this->value);
	}
	
	public function setValue($value){
		$this->value=$value;
	}
	
	public function __toString(){
		return (string)$this->getValue();
	}
	
	public function add($addDegrees){
		return $this->temperatureUnit->add($addDegrees);
	}
	public function sub($subDegrees){
		return $this->temperatureUnit->sub($subDegrees);
	}
	public function addToSeft($addDegrees){
		$this->temperatureUnit->addToSeft($addDegrees);
	}
	public function toCelsius(){
		return $this->temperatureUnit->toCelsius();
	}
	public function toFahrenheit(){
	   return $this->temperatureUnit->toFahrenheit(); 
	}
	public function toKelvin(){
		return $this->temperatureUnit->toKelvin(); 
	}
}

class Celsius extends TemperatureDegrees{
	public function __construct($value){
		parent::__construct($value,new TemperatureUnitCelsius());
	}
}

class Fahrenheit extends TemperatureDegrees{
	public function __construct($value){
		parent::__construct($value,new TemperatureUnitFahrenheit());
	}
}
class Kelvin extends TemperatureDegrees{
	public function __construct($value){
		parent::__construct($value,new TemperatureUnitKelvin());
	}
}
	

class TemperatureUnit{

	public function setTemperatureDegrees($degrees){
		$this->degrees=$degrees;
	}
	
	protected function getName(){
		return  substr(get_class($this),strpos(get_class($this),'Unit')+4);
	}
	
	public function add($addDegrees){
		$class=$this->getName();
		$method='to'.$this->getName();
		return new $class($this->degrees->getValue()+$addDegrees->$method()->getValue());
	}
	public function sub($subDegrees){
		$class=$this->getName();
		$method='to'.$this->getName();
		return new $class($this->degrees->getValue()-$subDegrees->$method()->getValue());
	}
	
	public function subToSeft($subDegrees){
		$class=$this->getName();
		$method='to'.$this->getName();
		$this->degrees->setValue(new $class($this->degrees->getValue()-$subDegrees->$method()->getValue()));
		return $this->degrees;
	}
	public function addToSeft($addDegrees){
		$class=$this->getName();
		$method='to'.$this->getName();
		$this->degrees->setValue(new $class($this->degrees->getValue()+$addDegrees->$method()->getValue()));
		return $this->degrees;
	}
}
class TemperatureUnitCelsius extends TemperatureUnit{
	
	public function toCelsius(){
		return $this->degrees;
	}
	public function toFahrenheit(){
	    return new Fahrenheit($this->degrees->getValue() * (9 / 5) + 32);
	}
	public function toKelvin(){
		return new Kelvin($this->degrees->getValue() + 273.15);
	}
}

class TemperatureUnitFahrenheit	 extends TemperatureUnit{	
	public function toCelsius(){
		return new Celsius(($this->degrees->getValue() -32) * 5/9); 
	}
	public function toFahrenheit(){
		return new Fahrenheit($this->degrees->getValue());
	}
	public function toKelvin(){
	   return new Kelvin(($this->degrees->getValue() + 459.67) * 5/9);
	}

}

class TemperatureUnitKelvin	 extends TemperatureUnit{	
	public function toCelsius(){
		return new Celsius($this->degrees->getValue() - 273.15);
	}
	public function toFahrenheit(){
		return new Fahrenheit($this->degrees->getValue() * (9/5) - 459.67);
	}
	public function toKelvin(){
		return new Kelvin($this->degrees->getValue());
	}

}




$celsius=new Celsius(-150);
echo $celsius . 'C<br/>';
echo $celsius->toFahrenheit(). 'F<br/>';
echo $celsius->toKelvin() . 'K<br/>';
echo '<br/>';
$fahrenheit=new Fahrenheit(123);
echo $fahrenheit . 'F<br/>';
echo $fahrenheit->toCelsius(). 'C<br/>';
echo $fahrenheit->toKelvin(). 'K<br/>';
echo '<br/>';
$kelvin=new Kelvin(9.15);
echo $kelvin .'K<br/>';
echo $kelvin->toCelsius().  'C<br/>';
echo $kelvin->toFahrenheit().'F<br/>';

$result=$celsius->add($celsius)
				->add($celsius->toFahrenheit())
				->add($celsius->toKelvin())
				->add($fahrenheit)
				->add($fahrenheit->toCelsius())
				->add($fahrenheit->toKelvin())
				->add($kelvin)
				->add($kelvin->toCelsius())
				->add($kelvin->toFahrenheit())
				->sub(new Fahrenheit(1000));
echo '<br/>';		
echo $result . 'C<br/>';
echo $result->toFahrenheit(). 'F<br/>';
echo $result->toKelvin() . 'K<br/>';