CODEWITHSUNDEEP
c#inheritancecontainersupcasting
Titan
Titan

Reputation: 191

inheritance and container in C#

I work in C# here, let's say i have:

class A
{}

class B : A
{}

List<B> myList;

I would like, in a part of the code cast this myList as List< A>, but when I try to, I get an error:

List<A> myUpcastedList = (List<A>)myList; //not working

is it possible to do it ? if yes, what is the syntax ?

Upvotes: 3

Views: 842

Answers (5)

Eric Lippert
Eric Lippert

Reputation: 660289

A list of tigers cannot be used as a list of animals, because you can put a turtle into a list of animals but not into a list of tigers.

In C# 4 and 5 this is legal if you use IEnumerable<T> instead of List<T> because there is no way to put a turtle into a sequence of animals. So you can say:

List<B> myList = new List<B>();
IEnumerable<A> myUpcastedList = myList; // legal

Upvotes: 3

MarcinJuraszek
MarcinJuraszek

Reputation: 125640

List<B> cannot be casted to List<A>. You have to create new List<A> and fill it with items from source commection. You can use LINQ to Objects for that:

var aList= bList.Cast<A>().ToList();

You should also read a bit about covariance and contravariance, e.g. on Eric Lippert’s Blog

Upvotes: 5

user1968030
user1968030

Reputation:

You can use this question maybe useful for you

List<A> testme = new List<B>().OfType<A>().ToList();

Upvotes: 1

David Hope
David Hope

Reputation: 2256

I was able to:

List<A> myUpcastedList = myList.ToList<A>();

this makes a copy of the list though... not sure that's what you intended

Upvotes: 1

Peter Karlsson
Peter Karlsson

Reputation: 1180

As far as I'm aware this is not possible. An alternative would be to do the following.

using System.Linq;

var myUpcastedList = myList.Cast<A>().ToList();

Upvotes: 1

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