Question

I have a model whereby I have an abstract class (lets call it Vehicle) and several inherited classes, such as Bike, Motorbike, Car, Van etc. This is essentially a simplified version of a real world problem.

abstract class Vehicle
    int ID;
    int WheelCount;
    string OwnerName;

class Bike
    DateTime lastSafetyCheck;

class Motorbike
    int EngineCC

class Car
    double EngineSize

class Van
    double StorageCapacity

I have within my system an IEnumerable<Vehicle> which contains each of these. This is contained in a thread safe singleton class, essentially acting as an in-memory database.

I wish to have a method in my application (in either the singleton or a seperate class) which allows me to query for only a certain type of Vehicle.

Initially I considered a method like:

internal IEnumerable<T> GetVehicles<T>() where T : Vehicle

in order that I would be able to supply a type T which would specify the type I wish to retrieve. I know that I can then use typeof() in order to perform logic. But what I cannot figure out is how to return my values? I’m basically struggling with the contents of the method, and I am beginning to think there must be a design pattern out there which would make a lot more sense.

AK

Answer 1

LINQ already has this method – OfType:

var vans = Vehicales.OfType<Van>();

As an aside, to determine whether an instance is an instance of a type you do not need to use typeof(), you can use the is and as operators (and they can be used with generic types also):

if (vehicle is Van) ...
if (vehicle is T) ...

Or

var van = vehicle as Van;
if (van != null) ...

var instance = vehicle as T; // Will need T : class generic type constraint
if (instance != null) ...

var instance = vehicle as T?; // Will need T : struct generic type constraint
if (instance != null) ...