Re: How do you return a subclass instance from a base class method?
On Thursday, 17 November 2022 at 06:48:13 UTC, Daniel Donnelly, Jr. wrote: On Thursday, 17 November 2022 at 05:21:05 UTC, MorteFeuille123 wrote: On Thursday, 17 November 2022 at 04:25:13 UTC, Daniel Donnelly, Jr. wrote: [...] You can use TypeInfoClass: [...] I don't get it - you never made use of b1 or b2... yeah this was oversimplified on purpose, I did not realize that this coulmd be confusing. I dont know what you do with your constructor parameter either, would I say, as a second explanation.
Re: How do you return a subclass instance from a base class method?
On Thursday, 17 November 2022 at 04:25:13 UTC, Daniel Donnelly,
Jr. wrote:
I have SubclassOf derived from PosetRelation. For any poset
relation, the transitivity law applies, however, I'd like to
return the correct type:
How does one accomplish this in D? Because PosetRelation
doesn't know about SubclassOf, in general.
You can use TypeInfoClass:
```d
class Base
{
}
class Derived : Base
{
}
Object newDerivedFromTi(Base b)
{
return typeid(b).create();
}
void main(string[] args)
{
Base b = new Base;
Base d = new Derived;
assert(cast(Derived)newDerivedFromTi(d));
}
```
But that only works with default constructors, i.e no parameters.
Another way is to define a virtual function in the Base:
```d
class Base
{
Object createMostDerived(Base b1, Base b2)
{
return new typeof(this);
}
}
class Derived : Base
{
override Object createMostDerived(Base b1, Base b2)
{
return new typeof(this);
}
}
Object newDerivedFromTi(Base b)
{
return b.createMostDerived(b, b);
}
void main(string[] args)
{
Base b = new Base;
Base d = new Derived;
assert(cast(Derived)newDerivedFromTi(d));
}
```
assuming the PosetRelation (here called Base) actually cary the
SubclassOf type (here called Derived).
