Cloning Derived Types In a Single Method

Question

I have a non Abstract Base class Vehicle which has three derived types.

Car
Motorcycle
Tractor

I am looking at a service called VehicleBuilder Which would have a method CloneVehicle which takes a parameter of Vehicle type and returns a cloned object for all three derived types.

Here's my CloneVehicle

public Vehicle CloneVehicle (Vehicle v)
{
   var newVehicle = ClonebaseVehicle(v); // Clones all the types in the Base class
   if(Vehicle.Type == Vehicles.Tractor)
    {
        // Clone individual fields
        var tractor = new Tractor();
        tractor = newVehicle as Tractor;
        tractor.TractorCapacity  = 50 ; // tractor is coming null here
        return tractor; 
    }
}

I want to reuse ClonebaseVehicle and cannot create a constructor as the classes are coming from a diferrent DLL. Any other ways where I can clone the dervied objects using a base class reference ?

I cannot change the Vehicle class or any of its derived classes to create an abstract method in it

Why is this assignment `tractor = newVehicle as Vehicle;` not `tractor = newVehicle as Tractor;`? — Romano Zumbé, Jul 18 '17 at 06:54
And why is this `if(Vehicle.Type == Vehicles.Tractor)` not this `if(v.Type == Vehicles.Tractor)` — Romano Zumbé, Jul 18 '17 at 06:55
Also related: https://stackoverflow.com/questions/8631898/c-sharp-inheritance-derived-class-from-base-class — MakePeaceGreatAgain, Jul 18 '17 at 06:55
How do you even determine the right type? Does your `CloneVehicle`-method really provide **three instances** or just *one* instance of a given types (from which three exist)? — MakePeaceGreatAgain, Jul 18 '17 at 06:57
@HimBromBeere I just need a method which would clone all three types of instances of my derived Classes — SJMan, Jul 18 '17 at 07:00
Are your classes **serializable**? If answer is yes then the most easy way to _clone_ an unknown object is to serialize it into a `MemoryStream` with `BinaryFormatter` and then deserialize a new instance. — Adriano Repetti, Jul 18 '17 at 07:11
@AdrianoRepetti I suppose OP also wants to change the type of an instance, not just clone an exitsing `Tractor`. — MakePeaceGreatAgain, Jul 18 '17 at 07:16

score 3 · Accepted Answer · answered Jul 18 '17 at 07:13

Within your CloneBaseVehicle-method you should provide all members from your base-class. If there are many members you may also use reflection to do this:

Vehicle CloneBaseVehicle(Vehicle v)
{
    Tractor t;
    switch v.Type
    {
        case Vehicles.Tractor:
            t = new Tractor();
        case Vehicles.Car:
            t = new Car();
        case Vehicles.Motorcycle:
            t = new Motorcycle();
    }

    // now copy the common properties
    t.MyProperty = v.MyProperty;
    t.AnotherProperty = v.AnotherProperty;

    return t;
}

public Vehicle CloneVehicle (Vehicle v)
{
    var newVehicl = CloneBaseVehicle();

    switch(v.Type)
    {
        case(Vehicles.Tractor):
            var tractor = newVehicle as Tractor;
            tractor.TractorCapacity  = 50 ;
            break;
        case Car:
            ...
            break;
    }
    return newVehicle;
}

A reflection-based approach for CloneBaseVehiclecould look like this:

Vehicle CloneBaseVehicle(Vehicle v)
{
    Tractor t;
    switch v.Type
    {
        case Vehicles.Tractor:
            t = new Tractor();
        case Vehicles.Car:
            t = new Car();
        case Vehicles.Motorcycle:
            t = new Motorcycle();
    }

    var properties = typeof(Vehicle).GetProperties();
    foreach(var p in properties)
        p.SetValue(t, v.GetValue(p));

    return t;
}

No matter which of the two approaches you chose you should be aware that when creating a Tractor from an existing Car you´re of course loosing all the special information that existed only in Car.

Cloning Derived Types In a Single Method

1 Answers1