Dynamic templated virtuals - I still often want them

[Tove]

On Thursday, 23 July 2020 at 10:18:34 UTC, Arafel wrote:
> On 23/7/20 11:51, Tove wrote:
>> It compiles but doesn't work, in your link you compiled with 
>> "-c", so the runtime assert was never evalutated.
>
> Ups! Sorry, I feel quite dumb now... I had the `-c` left from 
> some previous tests and didn't notice.
>
> I have indeed reviewed my code, and the caller is also 
> templated on the actual class, i.e., it's also calling the 
> method with the derived type.
>
> And in fact, now that I think about it, it can't possibly work 
> at compile time. Consider:
>
> ```
> Base b = uniform(0,2) ? new Base() : new Derived();
> ```
>
> This can obviously not be resolved at compile time (where the 
> template `this` parameter works).
>
> For runtime resolution you can already use `typeid(this)`, and 
> this (this time yes) works:
>
> ```
> module foo;
>
> import std;
>
> class Base {
>      string serialize() {
>          return typeid(this).toString; // just for example
>      }
> }
>
> class Derived : Base {
>
> }
>
> void main() {
> 	Base b = new Derived();
>     assert(b.serialize == "foo.Derived");
> }
> ```

Yes, this works fine. It has at least two issues though.

1) Slower than a virtual function call, but I suppose the result 
of typeid could be cached to mitigate this issue.

2) TypeInfo cannot be used with -betterC