[cxx-interop] Add CxxConvertibleToCollection protocol
#62243
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Since we don't automatically conform C++ non-random-access collections to `Swift.Sequence` anymore for performance reasons, we need an alternative way to access the elements of a C++ sequence from Swift. This allows explicitly converting a C++ sequence to a Swift Array/Set.
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very cool, finally! :-) |
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It would be really cool if we could provide optimized implementations for contiguous collections (C++ provides this information in iterator traits). This could just be a reserve + memcpy. I don't know if LLVM is smart enough to do that on its own (probably not).
That can be a follow up patch, though.
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Great point! I'll do that in a separate patch.
| public init<C: CxxConvertibleToCollection>(_ c: C) | ||
| where C.RawIterator.Pointee == Element { | ||
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| self.init() |
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Can we reserve N elements here so we don't have to potentially allocate each time?
(Can also be follow up. And it would be cool if we had some benchmarks to measure if there's actually an improvement from that change/others.)
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Can we reserve N elements here so we don't have to potentially allocate each time?
We could do that for C++ RAC, however, C++ RAC are auto-conformed to Swift.RandomAccessCollection which brings an equivalent initializer. For non-random-access collections, we don't really know what N is until we actually iterate over the collection. For some collections iterating twice might produce different results so we can't do that I think.
it would be cool if we had some benchmarks to measure if there's actually an improvement from that change/others
This won't be an improvement unfortunately, we're just making the copy explicit. It's a good idea to add a benchmark though 👍
Since we don't automatically conform C++ non-random-access collections to
Swift.Sequenceanymore for performance reasons, we need an alternative way to access the elements of a C++ sequence from Swift.This allows explicitly converting a C++ sequence to a Swift Array/Set.
Auto-conformance logic will be added in a follow-up patch.