Create instance of object with Generics

Question

I have the following:

public class Query : IAsyncRequest<Envelope<Reply>> { }

public class Reply { }

public class Flow<TQuery, TReply> where TQuery: IAsyncRequest<Envelope<TReply>>, IRequest<Envelope<TReply>> {

  public TQuery Query { get; set; }
  public TReply Reply { get; set; }

  public Flow(TQuery query, TReply reply) {
    Query = query;
    Reply = reply;
  }
}

When I try to create an instance of Flow as

Query query = service.GetQuery();
Reply reply = service.GetReply();
Flow flow = new Flow(query, reply);

I get the error:

Using the generic type 'Flow<TQuery, TReply>' requires 2 type arguments

Can't I create a Flow this way?

Possible duplicate of Why can't the C# constructor infer type? — NineBerry
– NineBerry, Commented Oct 9, 2016 at 14:25

Community · Accepted Answer · 2017-05-23 10:27:48Z

2

No you can't, as said in @NineBerry's answer, the syntax new type must be the "real" type with mandatory generics arguments so you must write :

Flow<Query, Reply> flow = new Flow<Query, Reply> (query, reply);

That said, that constraint doesn't apply to a method, so you could write a static method to do the job :

static class Flow // not generic (same name isn't mandatory)
{
    public static Flow<TQuery, TReply> Create (TQuery query, TReply, reply) where /* constraint */
    {
        return new Flow<TQuery, TReply> (query, reply);
    }
}

// usage
Flow<Query, Reply> flow = Flow.Create (query, reply);
// or with var
var flow = Flow.Create (query, reply);

edited May 23, 2017 at 10:27

CommunityBot

11 silver badge

answered Oct 9, 2016 at 14:29

Sehnsucht

5,05919 silver badges27 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Bernhard Koenig Over a year ago

Ah, Factory pattern to the rescue :) ... nice alternative.

Community · Accepted Answer · 2017-05-23 11:55:13Z

1

You need to specify the types explicitly. Type inference is not supported here. See also Why can't the C# constructor infer type?

Query query = service.GetQuery();
Reply reply = service.GetReply();
var flow = new Flow<Query, Reply>(query, reply);

edited May 23, 2017 at 11:55

CommunityBot

11 silver badge

answered Oct 9, 2016 at 14:26

NineBerry

28.8k4 gold badges68 silver badges104 bronze badges

2 Comments

Sehnsucht Over a year ago

you forgot generic arguments on the first Flow (flow's type) ;)

NineBerry Over a year ago

@Sehnsucht Thanks. Fixed

Bernhard Koenig · Accepted Answer · 2016-10-09 14:29:47Z

0

No, you have to define the types you want to use:

Flow<Query, Reply> flow = new Flow<Query, Reply>(query, reply);

C# constructors do not support type inference.

edited Oct 9, 2016 at 14:29

answered Oct 9, 2016 at 14:27

Bernhard Koenig

1,40214 silver badges23 bronze badges

2 Comments

Sehnsucht Over a year ago

you forgot generic arguments on the first Flow (flow's type) ;)

Bernhard Koenig Over a year ago

Thanks :) ... I fixed that.

Collectives™ on Stack Overflow

Create instance of object with Generics

3 Answers 3

1 Comment

2 Comments

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

2 Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related