C# constructor in interface

Question

I know that you can't have a constructor in an interface, but here is what I want to do:

 interface ISomething 
 {
       void FillWithDataRow(DataRow)
 }


 class FooClass<T> where T : ISomething , new()
 {
      void BarMethod(DataRow row)
      {
           T t = new T()
           t.FillWithDataRow(row);
      }
  }

I would really like to replace ISomething's FillWithDataRow method with a constructor somehow.

That way, my member class could implement the interface and still be readonly (it can't with the FillWithDataRow method).

Does anyone have a pattern that will do what I want?

duplicate - have a look here stackoverflow.com/questions/619856/… — Blounty
– Blounty, Commented Nov 6, 2009 at 8:25
Possible duplicate of Interface defining a constructor signature? — Nisarg Shah
– Nisarg Shah, Commented Oct 26, 2017 at 13:23

NDM · Accepted Answer · 2022-08-25 14:46:34Z

9

use an abstract class instead?

you can also have your abstract class implement an interface if you want...

interface IFillable<T> {
    void FillWith(T);
}

abstract class FooClass : IFillable<DataRow> {
    public void FooClass(DataRow row){
        FillWith(row);
    }

    protected void FillWith(DataRow row);
}

edited Aug 25, 2022 at 14:46

answered Nov 6, 2009 at 8:24

NDM

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Community · Accepted Answer · 2017-05-23 12:08:23Z

(I should have checked first, but I'm tired - this is mostly a duplicate.)

Either have a factory interface, or pass a Func<DataRow, T> into your constructor. (They're mostly equivalent, really. The interface is probably better for Dependency Injection whereas the delegate is less fussy.)

For example:

interface ISomething 
{      
    // Normal stuff - I assume you still need the interface
}

class Something : ISomething
{
    internal Something(DataRow row)
    {
       // ...
    }         
}

class FooClass<T> where T : ISomething , new()
{
    private readonly Func<DataRow, T> factory;

    internal FooClass(Func<DataRow, T> factory)
    {
        this.factory = factory;
    }

     void BarMethod(DataRow row)
     {
          T t = factory(row);
     }
 }

 ...

 FooClass<Something> x = new FooClass<Something>(row => new Something(row));

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