On Wed, Feb 22, 2017 at 04:08:45PM +0000, Stefan Koch via Digitalmars-d-learn wrote: > On Wednesday, 22 February 2017 at 15:27:22 UTC, H. S. Teoh wrote: > > (In fact, now I'm wondering if we could just hack dmd to emit the > > equivalent of this code as a lowering, whenever the user tries to > > declare a compile-time initialized AA.) > > All the problems disappear if the AA's are compiler visible and > CTFEable code.
I'm not sure it's that simple. Just because AA's become CTFEable doesn't mean they will automatically be convertible to object code in the executable that allows runtime AA lookups. For instance, a CTFE pointer will have a value that has no correspondence with the object code in the executable, and neither will memory allocated during CTFE have any correspondence with the emitted object code (because this memory is allocated in the compiler, not in the object code). So if the CTFE AA implementation allocates nodes for storing key/value pairs, they will only exist in the CTFE engine, and pointers to them will only make sense within the CTFE engine. In order to make them work in the executable (so that you can do AA lookups to these computed nodes at runtime), you will need to somehow map them to object code. Just because AA's become CTFEable will not automatically solve this for you. > There is as far as I know a project by Martin Nowak that does that. > And uses templates for AA's rather then whacky TypeInfos. > > So in the future this problem will disappear. Oh I know, the problem is that this "future" has been taking a long time arriving. I was involved in an early (but unfortunately unsuccessful) effort to rewrite AA's as library code. But there was simply too much compiler magic involved with AA's that it couldn't work at the time. Much of this magic has been dispelled over the past few years, though, so we should be in better shape now for moving AA's completely into the library. I'm very much looking forward to Martin's implementation when it's ready. But in the meantime, lowering compile-time initialized AA's could have the above hack as a temporary workaround until we can get AA literals to be embeddable in object code. T -- GEEK = Gatherer of Extremely Enlightening Knowledge
