Cast List to List

Question

I want to to cast a list of object type A to a list of object type B, where A inherit B.

Concretely :

public class A : B
{
    public string name { get; set; }
}

public class B
{
    public B() { }
}

I parse a JSON string that I cast to my list of type A :

B elem = ((JArray)_configuration).ToObject<List<A>>();

And I have this error :

Cannot implicitly convert type 'System.Collections.Generic.List< A>' to 'System.Collections.Generic.List< B>'

I tried to cast it :

List<B> elem = (List<B>)((JArray)_configuration).ToObject<List<A>>();

but got this error :

Cannot convert type 'System.Collections.Generic.List< A>' to 'System.Collections.Generic.List< B>'

I couldn't find help, maybe because I don't know what to look for, so apologies if it has been answered somewhere already !

http://stackoverflow.com/questions/5115275/cast-listx-to-listy The thing is you'll need to cast them individually, because [collections don't behave like you think they do](http://coding-time.blogspot.co.uk/2011/05/covariance-and-contravariance-simple.html). — Nathan Cooper, Oct 22 '15 at 09:53
Possible duplicate of [Convert List to List](http://stackoverflow.com/questions/1817300/convert-listderivedclass-to-listbaseclass) — Nikita Shrivastava, Oct 22 '15 at 09:54
Do you need the output to be a `List`? If you just need to read from the list you can do `IReadOnlyList l = inputList`. — Lee, Oct 22 '15 at 09:54

Jeroen van Langen · Accepted Answer · 2015-10-22T10:56:25.860

2

You can use the Enumerable.Cast<>() for this.

List<B> list = myList.Cast<B>().ToList();

But the ToList() will create a copy. If you just want for iterate the items. Don't use the ToList() and handle it as an IEnumerable<B>. It will be cast lazy 'on-the-fly'

edited Oct 22 '15 at 10:56

answered Oct 22 '15 at 09:53

Jeroen van Langen

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Thanks, I think this solution is better than the one I've found – carndacier Oct 22 '15 at 09:54

score 0 · Answer 2 · answered Oct 22 '15 at 09:53

0

Ok, just found the answer if it can help. If not, tell me and I will remove the question. Sorry for that !

Just needed to do :

List<B> elem = new List<B>(((JArray)_configuration).ToObject<List<A>>());

answered Oct 22 '15 at 09:53

carndacier

960
15
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There is no need to remove your question, instead, you should wait for couple of days and accept your own answer. – User2012384 Oct 22 '15 at 09:54
you can also do List elem=>(((JArray)_configuration).ToObject>().Cast().ToList() – user995219 Oct 22 '15 at 09:56

score 0 · Answer 3 · edited May 23 '17 at 12:29

0

maybe you should read this, use list.selectall.

you can also try this for arrays.

edited May 23 '17 at 12:29

Community

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answered Oct 22 '15 at 09:55

LiranBo

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Cast List to List

3 Answers3