• Ruby The Roobster (38/38) May 06 2022 Define an interface that has a function that returns an object of
• Ruby The Roobster (2/5) May 06 2022 Nevermind. I was being stupid and made a naming error.
• Salih Dincer (33/34) May 06 2022 What version compiler are you using? I've tried it in two

Ruby The Roobster <michaeleverestc79 gmail.com> writes:

Define an interface that has a function that returns an object of 
the same type:

```d
interface I
{
     I foo();
}
```

Now define a class that inherits that interface:

```d
class M : I
{
     this(int i)
     {
         this.i = i;
     }
     M foo()
     {
         return new M(42);
     }
     int i;
}
```

Given this example, the following main function fails to compile:

```d
void main()
{
     M m = new M(3);
     M c = m.foo();
     import std.stdio;
     writeln(c.i);
}
```

The error message is the following:

```
Error: need `this` for `foo` of type `M()`
```

Why does this happen and how to fix it?

Ruby The Roobster <michaeleverestc79 gmail.com> writes:

On Saturday, 7 May 2022 at 00:48:20 UTC, Ruby The Roobster wrote:
 Define an interface that has a function that returns an object 
 of the same type:
 ..

Nevermind.  I was being stupid and made a naming error.

Salih Dincer <salihdb hotmail.com> writes:

On Saturday, 7 May 2022 at 00:48:20 UTC, Ruby The Roobster wrote:
 Why does this happen and how to fix it?

What version compiler are you using?  I've tried it in two 
different versions (one is the newest), it works:

```d
import std;
interface I
{
     I foo();
}
class M : I
{
     this(int i)
     {
         this.i = i;
     }
     M foo()
     {
         return new M(42);
     }
     int i;
}
void main()
{
     M m = new M(3);
     m.i.writeln("(m.i)");
     M c = m.foo();
     c.i.writeln("(c.i)");
}/*Printouts:
3(m.i)
42(c.i)

Process finished.
*/
```