sumtypes for D

[Timon Gehr]

On 11/30/22 00:56, Vladimir Panteleev wrote:
> On Monday, 28 November 2022 at 09:27:11 UTC, Walter Bright wrote:
>> I've written most of a DIP for one. Should I:
> 
> I really wish that instead of adding more language features, we would 
> improve the language so that things like this are implementable *in* the 
> language.

Well, ideally both. Tagged unions are fundamental enough to get some 
syntactic sugar. So are tuples. But except for syntax, I agree that 
user-defined types should be able to benefit as well.

Here, I guess this would mean to add some mechanism to allow the 
language to understand which `union` member is currently active. This 
would also help with precise GC.

Another consideration is compile times. Sometimes it makes sense to 
build things into the language because you don't want to interpret them 
again and again if you can compile them once into the compiler frontend.

I also don't like magic though. Ideally it should be possible to write a 
shallow wrapper `struct` (template) around any other type without losing 
any functionality.