Constructor is not callable using argument types

[Mike Parker via Digitalmars-d-learn]

On Tuesday, 8 August 2017 at 06:03:06 UTC, Nrgyzer wrote:
> Hi guys,
>
> I've the following code:
>
> abstract class a {}
> class b : a { this(a* myAttr = null) {} }
> class c : a { this(a* myAttr = null) {} }
>
> void main()
> {
>     auto myb = new b();
>     auto myc = new c(&myb);
> }
>
> DMD says "Constructor c.this(a* myAttr = null) is not callable 
> using argument types (b*)". I'm confused why it fails because 
> class b and c are both derived from class a and the constructor 
> of class b accepts a pointer of class a.
>
> When I replace "auto myb = new b();" by "a myb = new b();", it 
> works as expected. But then I cannot class-specific functions 
> of class b because I've the instance of the base-class a. So, 
> what's the correct way?

Don't use pointers. Classes are already reference types:

abstract class a {}
class b : a { this(a myAttr = null) {} }
class c : a { this(a myAttr = null) {} }

void main()
{
     auto myb = new b();
     auto myc = new c(myb);
}

If you pass class pointers around, you're passing pointers to the 
*references*, not to the *instances*. A b is always an a, but a 
b* is not an a* unless you cast. And anyway, it's almost 
certainly not what you want.