How do I cast in a LINQ query?

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Is there a way to use an explicit cast operator as a part of a LINQ query?

I have tried to show what I want to do with the code below. It is a somewhat contrived example because in a real application a Car would probably be a subclass of a Vehicle, but please pretend that for some reason a parent-subclass relationship is not appropriate. Also, for the sake of simplicity, assume I know all the vehicles are cars.

C#

public class Vehicle
{
}

public class Car
{
    public static explicit operator Car( Vehicle v )
    {
    }
}

public CarCache
{
    public IList<car> SomeCars
    {
        get
        {
            // Can I use a single LINQ query here to return the vehicles as cars? 
        }
    }

    private IEnumerable<vehicle> _vehicles;
}

I'm struggling to write the code indicated by the comment above. Can anyone help me out (if it is indeed possible)?

I'm fairly new to LINQ, so I apologise if the answer to this question is blindingly obvious.

What I have tried:

I have tried the usual Googling but no example I have been able to find seems to relate exactly to what I want to do.

Posted 16-Nov-16 5:41am

Patrick Skelton

Updated 16-Nov-16 6:17am

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3 solutions

Solution 1

Try this:

C#

List<Car> cars = carCache.Where(x=>x is Car).ToList<Car>();

Posted 16-Nov-16 5:51am

#realJSOP

Updated 16-Nov-16 5:53am

v2

Comments

OriginalGriff 16-Nov-16 11:58am

Psst! Does that compile for you?

#realJSOP 16-Nov-16 18:09pm

I dunno - I was in the middle on own work, and was kinda distracted.

Solution 2

Personally, I'd do it slightly differently:

C#

public class Vehicle
{
}
 
public class Car : Vehicle
{

What that means is that every Car is also a Vehicle, so you can store all Vehicle types in your cache:

C#

public class CarCache
     {
     public IList<Car> SomeCars
         {
         get
             {
             return _vehicles.Where(v => v is Car).Cast<Car>().ToList();
             }
         }
     private List<Vehicle> _vehicles = new List<Vehicle>();
     public void Add(Vehicle v) { _vehicles.Add(v); }
     }

(Don't store the collection as an IEnumerable: it doesn't have an Add method so it's difficult to change the content!)

Posted 16-Nov-16 5:55am

OriginalGriff

Comments

Midi_Mick 16-Nov-16 12:16pm

That works if Car inherits from Vehicle. However, his code shows an explicit cast defined, so it may be that Car is a member of Vehicle, and the explicit cast returns that member (which is why explicit casts are normally defined), in which case the above won't work. He'd need to leave out the "Where" under those circumstances.

OriginalGriff 16-Nov-16 12:29pm

That's partly why I'd derive the Car from the Vehicle - it makes everything work better. If you don't have a suitable root in common, you can't cast it - you'd have to create a new instance and populate it with the relevant info. But then, you'd even up with two different instances if you cast the same vehicle twice, so changes to one won't affect the other (and subsequent changes to the original vehicle won't affect either instance). Deriving is a better solution.

Richard Deeming 16-Nov-16 13:42pm

If you're going to add inheritance, it would be better to use the OfType method:
return _vehicles.OfType<Car>().ToList();

OriginalGriff 16-Nov-16 14:03pm

Excellent idea! I had either forgotten it completely or never learned that one... :O

Patrick Skelton 17-Nov-16 5:27am

Thank you for those replies. I have learnt a lot. One thing I have learnt is to choose less-confusing names for example classes. I should have chosen something different to 'Car' and 'Vehicle' because, as I mention in my question, the two types don't have a base-subclass relationship. I will know what to do if I do encounter that situation though. :)

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F-ES Sitecore · Accepted Answer · 2016-11-16T06:17:00

Solution 3

C#

public IList<Car> SomeCars
{
    get
    {
        return _vehicles.Select(v => (Car)v).ToList();
    }
}

Posted 16-Nov-16 6:17am

F-ES Sitecore