[Swift] C-String buffer pointer from array of Strings

withUnsafeCStringBufferPointer.swift

extension Array where Element == String {
    @inlinable
    public func withUnsafeCStringBufferPointer<R>(_ body: (UnsafeBufferPointer<UnsafePointer<CChar>?>) throws -> R) rethrows -> R {
        func translate(_ slice: inout Self.SubSequence,
                       _ offset: inout Int,
                       _ buffer: UnsafeMutableBufferPointer<UnsafePointer<CChar>?>,
                       _ body: (UnsafeBufferPointer<UnsafePointer<CChar>?>) throws -> R) rethrows -> R {
            guard let string = slice.popFirst() else {
                return try body(UnsafeBufferPointer(buffer))
            }
            
            return try string.withCString { cStringPtr in
                buffer.baseAddress!
                    .advanced(by: offset)
                    .initialize(to: cStringPtr)
                offset += 1
                return try translate(&slice, &offset, buffer, body)
            }
        }
        
        var slice = self[...]
        var offset: Int = 0
        let buffer = UnsafeMutableBufferPointer<UnsafePointer<CChar>?>.allocate(capacity: count)
        defer { buffer.deallocate() }
        return try translate(&slice, &offset, buffer, body)
    }
}

Usage:

let strings = ["A", "B", "C"]

strings.withUnsafeCStringBufferPointer { buffer in
    for ptr in buffer {
        dump(String(cString: ptr!))   
    }
}

Inspired by https://forums.swift.org/t/can-an-unsafebufferpointer-to-local-scope-array-outlive-its-own-reference/47070/8