PHP / OOP设计问题，最佳实践是什么？

Question

I'm using PHP 5.3. I have a Vehicle class. These classes have inherited from Vehicle: Car, SUV, Lorry.

I need to get an array holding a specific type of objects inherited from Vehicle. It can be an array of Cars, SUVs, etc...

The way I solved it was that I created a class named CarCollection with a static method, which returns the list of cars. Then a class named SUVCollection for SUV...

But if I were to add a new vehicle class (let's call it Airplane), then I would need to create a new AirPlaneCollection class. Is this a bad choice?

The goal: I'm looking for a way to implement this using only one class, VehicleCollection returns a list of Cars, SUV etc.

How can I know in the code that in this specific script the VehicleCollection::getVehicles() will return cars and not SUV? Maybe I can have some logic the class checking from where it was called, or I send in the caller object as a parameter, then check which class it is and according to that get VehicleCollection::getVehicles() to return for examle SUV and not Car.

Answer 1

You could try making your own collection type, which validates that everything is a vehicle, but also enforces they're all the same type of vehicle.

<?php
class Vehicle {}

class Car extends Vehicle {}

class SUV extends Vehicle {}

// This doesn't need to be an SplDoublyLinkedList, it's just
// a convenient datastructure to demo with
class VehicleCollection extends SplDoublyLinkedList
{
    public function add($index, Vehicle $obj)
    {
        $this->validateType($obj);
        parent::add($index, $obj);
    }

    public function push(Vehicle $obj)
    {
        $this->validateType($obj);
        parent::push($obj);
    }

    protected function validateType($obj)
    {
        // If we have anything in here, ensure next is the same vehicle type
        if (!($this->isEmpty() || $this->top() instanceof $obj)) {
            throw new InvalidArgumentException('Argument passed to ' . __CLASS__ . '::' . __FUNCTION__ . ' must all be instances of same type.');
        }
    }
}

// Make a new collection
$col = new VehicleCollection();

// Let's have a couple cars
$car = new Car;
$car2 = new Car;

// And an SUV
$suv = new SUV;

// Let's add our cars
$col->push($car);
$col->push($car2);

var_dump($col);
/* Collection right now:
class VehicleCollection#1 (2) {
  private $flags =>
  int(0)
  private $dllist =>
  array(2) {
    [0] =>
    class Car#2 (0) {
    }
    [1] =>
    class Car#3 (0) {
    }
  }
}
*/

// Now we try to add an SUV
$col->push($suv);

// and get this:
// PHP Fatal error:  Uncaught exception 'InvalidArgumentException' with message 'Argument passed to VehicleCollection::validateType must all be instances of same type.'

This has the added benefit that if you further extended, eg made a class SportsCar extends Car {} , that SportsCar could go into your collection.

It was pointed out that I might have been misinterpreting your question. If you're just trying to filter an array, this becomes a much simpler problem. I wouldn't bother to even implement a special class if that's the case - just pass a Closure into array_filter , which is quite readable and an easy pattern to follow elsewhere:

$vehicles = [$car, $suv, $car2];
$cars = array_filter($vehicles, function($vehicle) { return $vehicle instanceof Car; });
$suvs = array_filter($vehicles, function($vehicle) { return $vehicle instanceof SUV; });

So in that example, the array of vehicles has an SUV, and once filtered, the $cars array has only the cars. If you want to make that a class method, you could do something along the lines of:

public function getAllOfType($type)
{
    return array_filter(
        $this->vehicles,
        function($vehicle) { return is_a($vehicle, $type); }
    );
}

Then to grab only cars from your collection:

$cars = $myVehicleCollection->getAllOfType('Car');

Answer 2

What about a static property in the parent class Vehicle that would look something like:

array( 'cars' => array(car instances),
   'suvs' =>array(suv instances).
    ....
)

Then you would have to put logic in your constructors and destructors to add and remove the objects from this array.

Then you can get a list of all cars by calling Vehicle::thatArry['cars'] . But of course you want to throw some nice getters and setters around that array.

I haven't totally thought this through yet, it might need some tweaks. But if its totally off, holla at me.