How do I return null from generic function?

Question

I have function like this:

private T DeserializeStream<T>(Stream data) where T : IExtensible
    {
        try
        {
            var returnObject = Serializer.Deserialize<T>(data);
            return returnObject;
        }
        catch (Exception ex)
        {
            this.LoggerService.Log(this.AccountId, ex);
        }

        return null;
    }

Everything is good, except that it complains about return null; part

Cannot convert expression type 'null' to type 'T'

How do I return null from function like this?

You can return `default(T)` as answered in this post: http://stackoverflow.com/questions/302096/how-can-i-return-null-from-a-generic-method-in-c?rq=1 — mindandmedia, Jul 21 '12 at 20:58

score 7 · Accepted Answer · edited May 23 '17 at 11:48

7

You can add a generic constraint that T is a class (as structures are value types and cannot be null).

private T DeserializeStream<T>(Stream data) where T : class, IExtensible

As @mindandmedia commented, an alternative is to return the default of T - this will allow it to work on value types (such a Nullable<T>, int32 etc...).

edited May 23 '17 at 11:48

Community

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answered Jul 21 '12 at 20:57

Oded

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I put this as an answer and it was converted to a comment... – mindandmedia Jul 21 '12 at 21:00
@mindandmedia - You didn't mention the generic constraint. You put a single sentence and a link - that got converted to a comment. If you put in a bit more, it would have remained as an answer. Just pointing out what seems to have happened. – Oded Jul 21 '12 at 21:01
@Oded the order is class, IExtensible – HatSoft Jul 21 '12 at 21:02
it's ok, i still get sweet karma(?) from the comment... :) – mindandmedia Jul 21 '12 at 21:02
@CodesInChaos - Probably got converted automatically. There are some heuristics for that which do not involve any mod. – Oded Jul 21 '12 at 21:03
@Oded Sounds plausible. A SO mod converting a post withing 3 minutes looked certainly strange. – CodesInChaos Jul 21 '12 at 21:04
@Oded this is how it should be where T : class, IExtensible the class comes first – HatSoft Jul 21 '12 at 21:05
@HatSoft - True. Was typing and my internal Syntax Error failed. – Oded Jul 21 '12 at 21:06

How do I return null from generic function?

1 Answers1