withUnsafeElementBufferPointer.swift

/// Calls the given closure with a buffer over the given tuple's elements.
///
/// - Parameters:
///   - tuple: The tuple.
///   - elementType: The type of all of the elements in the tuple.
///   - body: The closure to execute.
///
/// - Returns: The result of `body`, if any.
func withUnsafeElementBufferPointer<Tuple, Element, Result>(
    of tuple: Tuple,
    elementType: Element.Type,
    body: (UnsafeBufferPointer<Element>) throws -> Result
) rethrows -> Result {
    assert(
        MemoryLayout<Tuple>.stride.isMultiple(of: MemoryLayout<Element>.stride),
        "Incompatible tuple and element types.")
    let count = MemoryLayout<Tuple>.stride / MemoryLayout<Element>.stride
    return try withUnsafeBytes(of: tuple) { bytes -> Result in
        let start = bytes.baseAddress!.assumingMemoryBound(to: Element.self)
        return try body(.init(start: start, count: count))
    }
}

let x = (1, 2, 3, 4)
let sum = withUnsafeElementBufferPointer(of: x, elementType: Int.self) {
  $0.reduce(0, +)
}