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[cxx-interop] Proper conversions between MutableSpan and C++ span #81097

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Merged
merged 1 commit into from
Apr 25, 2025
Merged

[cxx-interop] Proper conversions between MutableSpan and C++ span #81097

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16 changes: 13 additions & 3 deletions stdlib/public/Cxx/CxxSpan.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -12,8 +12,8 @@
import Builtin

@usableFromInline
internal func unsafeBitCast<T: ~Escapable, U>(
_ x: T, to type: U.Type
internal func unsafeBitCast<T: ~Escapable & ~Copyable, U>(
_ x: consuming T, to type: U.Type
) -> U {
Builtin.reinterpretCast(x)
}
Expand Down Expand Up @@ -139,7 +139,7 @@ public protocol CxxMutableSpan<Element> {
init(_ unsafeMutablePointer : UnsafeMutablePointer<Element>, _ count: Size)

func size() -> Size
func __dataUnsafe() -> UnsafeMutablePointer<Element>
func __dataUnsafe() -> UnsafeMutablePointer<Element>?
}

extension CxxMutableSpan {
Expand All @@ -150,4 +150,14 @@ extension CxxMutableSpan {
"UnsafeMutableBufferPointer should not point to nil")
unsafe self.init(unsafeMutableBufferPointer.baseAddress!, Size(unsafeMutableBufferPointer.count))
}

@available(SwiftStdlib 6.2, *)
@inlinable
@unsafe
public init(_ span: consuming MutableSpan<Element>) {
let (p, c) = unsafe unsafeBitCast(span, to: (UnsafeMutableRawPointer?, Int).self)
unsafe precondition(p != nil, "Span should not point to nil")
let binding = unsafe p!.bindMemory(to: Element.self, capacity: c)
unsafe self.init(binding, Size(c))
}
}
24 changes: 24 additions & 0 deletions test/Interop/Cxx/stdlib/use-std-span.swift
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Expand Up @@ -687,6 +687,30 @@ StdSpanTestSuite.test("Convert between Swift and C++ span types")
expectEqual(cxxSpan[2], 3)
}
}
do {
var arr: [Int32] = [1, 2, 3]
arr.withUnsafeMutableBufferPointer{ ubpointer in
let s = SpanOfInt(ubpointer.baseAddress!, ubpointer.count)
let swiftSpan = MutableSpan(_unsafeCxxSpan: s)
expectEqual(swiftSpan.count, 3)
expectFalse(swiftSpan.isEmpty)
expectEqual(swiftSpan[0], 1)
expectEqual(swiftSpan[1], 2)
expectEqual(swiftSpan[2], 3)
}
}
do {
var arr: [Int32] = [1, 2, 3]
arr.withUnsafeMutableBufferPointer{ ubpointer in
let s = MutableSpan(_unsafeElements: ubpointer)
let cxxSpan = SpanOfInt(s)
expectEqual(cxxSpan.size(), 3)
expectFalse(cxxSpan.empty())
expectEqual(cxxSpan[0], 1)
expectEqual(cxxSpan[1], 2)
expectEqual(cxxSpan[2], 3)
}
}
}

runAllTests()