Is there other way to do that?

[evilrat]

On Monday, 15 February 2021 at 07:26:56 UTC, Jack wrote:
> I need to check if an instance is of a specific type derived 
> from my base class but this class has template parameter and 
> this type isn't available at time I'm checking it. Something 
> like:
>

Non-templated interface/base class is probably the only way I'm 
aware of, it is also how it is usually done with C# generics 
where needed for the same reason.

Even though typeid() knows the type I have no idea how to use it 
that way.


Interface adds 1 pointer to classinfo or vtbl, so it is increases 
instance size a bit.

```
import std;

class B { }
class A(T) : B { }
class X : B { }
class Z : B { }

interface IA {}
class AA(T) : B, IA {}

void main()
{
     writeln(__traits(classInstanceSize, AA!void)); // prints 24
     writeln(__traits(classInstanceSize, A!void)); // prints 16
}

```