Just FYI Implementation of Type Erasers https://lists.swift.org/pipermail/swift-dev/Week-of-Mon-20160905/002852.html
2017-04-05 22:22 GMT+09:00 Pavol Vaskovic via swift-dev <swift-dev@swift.org >: > On Wednesday, 5 April 2017 at 14:56, Pavol Vaskovic wrote: > > Thanks Ole! This explanation of type erasure makes total sense. I have > overlooked they are generic over different axis. > > > > But I think I have confirmed the performance implications of this design > and created https://bugs.swift.org/browse/SR-4499 to track the issue. > > As is, all elements that get vended through this are being created using > virtual dispatch on generic protocol - super slow. > > > > If I recall correctly, there is alternative approach to type erasure > using closures, but its possible it has similar performance characteristics? > Why exactly isn’t `AnyIterator` implemented like this? > > public struct AnyIterator<Element> : IteratorProtocol, Sequence { > let _next: () -> Element? > public init<I : IteratorProtocol>(_ base: I) where I.Element == Element { > var _base = base > _next = { return _base.next() } > } > public init(_ next: @escaping () -> Element?) { > _next = next > } > public func next() -> Element? { > return _next() > } > } > > > It seems to me this is using the same "Methods Constructed in > Initializers” pattern I was asking about Re: `_ClosureBasedIterator`. > > Best regards > Pavol Vaskovic > > > > _______________________________________________ > swift-dev mailing list > swift-dev@swift.org > https://lists.swift.org/mailman/listinfo/swift-dev >
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