Report: Swift and C++ interoperability project progress in the Swift-5.7 time frame

Development C++ interoperability
21

Stefan, following my related experimental code.
I tested ok using the Swift 5.8 development snapshot and also the trunk.

Package.swift

// swift-tools-version: 5.7

import PackageDescription

let package = Package(
    name: "SwiftCXXInteropExample",
    products: [
        .library(name: "MySwiftLib", type: .dynamic, targets: ["MySwiftLib"])
    ],
    dependencies: [],
    targets: [
        .target(name: "MySwiftLib", swiftSettings: [.unsafeFlags(["-enable-experimental-cxx-interop", "-emit-objc-header", "-Xfrontend", "-clang-header-expose-decls=all-public"])])
    ]
)

MySwiftLib/file.swift

// Ultra simple Swift library
// file.swift

import Foundation

// Expose a Swift function to C++
// The function must be public

// To expose _all_ the public functions, use the flag -Xfrontend -clang-header-expose-decls=all-public
// The @_expose attribute can be used to expose the function using a different name, useful when dealing with function overloads
// ref: https://github.com/apple/swift/blob/main/docs/CppInteroperability/UserGuide-CallingSwiftFromC%2B%2B.md

// Note: in the UserGuide this attribute looks like @expose(C++, foo) however,
// at least in the 5.8 and latest toolchain snapshot we must instead write @_expose(Cxx, "foo")

//@_expose(Cxx, "my_exposed_swift_add")
public func my_swift_add(a: Int64, b: Int64) -> Int64 {
    return a + b
}

$ swift build

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