On Tue, Feb 08, 2022 at 09:08:47PM +0000, tastyminerals via Digitalmars-d-learn wrote: [...] > > bool[E] works just fine. > > > > The bool does take up 1 byte, though, so if you're *really* want to > > optimize that away, you could do this: > > > > alias Unit = void[0]; > > enum unit = Unit.init; > > > > // Look, ma! A bona fide set! > > Unit[E] mySet; > > > > mySet[...] = unit; > > mySet.remove(...); > > ... // etc. > > > > Or you can wrap void[0][E] in a nice user-defined type that gives > > nice set-like syntax. But IMO, this is all overkill, and adds > > needless complexity. Just use bool[E] or std.container.rbtree. :-D [...] > Can you please explain what does `bool[E]` mean?
E is whatever key type you want to use. String, or integer ID, or whatever you want to put in your set. > And how does the code with aliasing void[0] and then using enum even > work? The alias is a workaround for a syntactic limitation in D, because you cannot write `mySet[someKey] = void[0].init;` without a syntax error. So we use the alias to give `void[0]` a name that we can refer to in assignment statements, so that we can assign its values to the AA. As for `void[0]` itself, it's just a zero-element static array of an indeterminate type. The whole point is to create something that occupies 0 bytes. The actual type doesn't actually matter; you could have used int[0] and it'd work too. (You can't use an empty struct because empty structs have size 1.) By using a zero-sized value type for the AA, we effectively turn it into a set: it only stores keys. Well, technically it stores values of zero size too, but since it's zero-sized, it's as if the value isn't there, and it incurs zero memory overhead. (Whereas an empty struct would likely occupy an entire machine word, rounded up from size 1.) But as I said, this is overkill for something so trivial. Using `bool[E]` or an RBTree works just fine. T -- Javascript is what you use to allow third party programs you don't know anything about and doing you know not what to run on your computer. -- Charles Hixson
