On Friday, 6 July 2018 at 12:31:50 UTC, FeepingCreature wrote:
On Friday, 6 July 2018 at 12:10:58 UTC, Simen Kjærås wrote:
The rest looks sensible to me, but I have to say this is
bollocks. This Nullable never has to construct an S.init:
struct Nullable(T) {
ubyte[T.sizeof] _payload;
bool _hasValue;
Come on, at least make it a union with a void[]. This way will
fail with any struct that requires a certain alignment. Not to
mention that you can stick a class in it and it'll be garbage
collected, because ubyte[] must not store pointers to GC memory.
Which makes the point, really - this is an utterly blatant,
unreliable, fragile hack.
The union brings back the exact problems we're trying to avoid.
It also makes it impossible to handle types where
hasElaborateAssign is true and this() is @disabled at the same
time. There's also the issue that at best it will do the wrong
thing when you @disable this() and init, but you probably
shouldn't do that anyway.
As for alignment, GC, and possibly other things, the code was not
intended as a complete implementation of Nullable, only to show
that an actual member of type T is not necessary. These issues
are fixable, if perhaps nontrivial in some cases.
--
Simen
