On Thursday, 12 July 2012 at 04:15:48 UTC, Andrei Alexandrescu
wrote:
Required reading prior to this: http://goo.gl/eXpuX
You destroyed, we listened.
I think Christophe makes a great point. We've been all thinking
inside the box but we should question the very existence of the
box. Once the necessity of opCmp, opEquals, toHash, toString is
being debated, we get to some interesting points:
Well, I'm not convinced it is a good idea to eliminate the stuff
from Object, nor to remove const (I think RawObject as a base
class of Object has merit, but to remove the Object functions for
everyone? I'm very suspicious.)
Some problems I would point out with the idea of "eliminate the
stuff from Object and use more templates instead":
1. Most importantly, the C++ template approach is a big pain for
large-scale systems, because in such systems you want to create
DLLs/SOs and C++ has neither a standard ABI nor a safe way to
pass around template instantiations between DLLs (in the presence
of changes to internal implementation details). Similar problems
exist for D, yes? It's a lot easier to define a standard ABI for
classes than to solve the cross-DLL template problem.
2. Although templates are used a lot in C++, in D programs they
are used even more and this proposal would increase template
usage, so I'd expect the bloat problem to increase. However,
merging identical functions (identical machine code) might be a
sufficient solution.
3. The need for more templates slows down compilation. We know
this is a huge problem in C++.
4. Template bloat is no big deal on desktops but it becomes a
bigger problem as the target system gets smaller. Maybe some
compromise should be made to ensure D remains powerful and
capable on small targets.
There were two proposals yesterday that I liked. Taken together,
they address all the problems that were raised with const
functions in Object:
1. Provide a 'safe workaround' for const, for caching and lazy
evaluation (implement it carefully to avoid breaking the
guarantees of immutable)
2. Provide a class modifier that makes immutable(_) illegal, so
the class uses "logical const" instead of "physical const".
