Thanks! That explains a lot.
In my version, performance only is improved by 10%, so I'm not sure if the
tradeoff is worth it:
In the isolated case of AnyIterator, there's only one method, so the sizeof
is the same (and the performance is worth it). In the case of AnySequence,
it would be a lot more work to write the implementation (and the size would
change a lot). Having two different mechanisms for type erasure seems like
it might confuse things even more.
On Mon, Sep 5, 2016 at 9:50 PM, Dmitri Gribenko <griboz...@gmail.com> wrote:
> On Mon, Sep 5, 2016 at 11:13 AM, Chris Eidhof via swift-dev
> <swift-dev@swift.org> wrote:
> > Hello swift-dev,
> >
> > I was wondering why type erasers (e.g. for AnyIterator) are implemented
> the
> > way they are. I would implement AnyIterator like this:
> >
> > final class MyAnyIterator<A>: IteratorProtocol {
> > var nextImpl: () -> A?
> >
> > init<I: IteratorProtocol>(iterator: I) where I.Element == A {
> > var copy = iterator
> > nextImpl = { copy.next() }
> > }
> >
> > func next() -> A? {
> > return nextImpl()
> > }
> > }
> >
> > Instead, it is implemented in a class which contains a box.
>
> Your approach requires adding a new closure property for every method
> that is forwarded. Subclassing does not require that.
>
> If you see a case where performance is not good, we would appreciate a
> bugreport at https://bugs.swift.org/ . Please attach a self-contained
> reproducer. Thank you.
>
> Dmitri
>
> --
> main(i,j){for(i=2;;i++){for(j=2;j<i;j++){if(!(i%j)){j=0;break;}}if
> (j){printf("%d\n",i);}}} /*Dmitri Gribenko <griboz...@gmail.com>*/
>
--
Chris Eidhof
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