Open Radar

 
Area:
Core Graphics

Summary:
CGPath.apply() has the following Swift signature:

    public func apply(info: UnsafeMutableRawPointer?, function: @escaping CoreGraphics.CGPathApplierFunction)

where CGPathApplierFunction is defined like this:

    public typealias CGPathApplierFunction = @convention(c) (UnsafeMutableRawPointer?, UnsafePointer<CGPathElement>) -> Swift.Void

All of these unsafe pointers make it difficult to write type-safe Swift code. In addition, the @convention(c) makes it impossible for the applier function to capture variables in its context, so it is necessary to define some sort of struct/class to pass data to the function and return results, and cast that to/from UnsafeMutableRawPointer.

CGPath.apply() should have a more Swift-friendly API, similar to that of the Array.forEach() function, which supports use of closures with captured variables, perhaps with a signature like this:

    func forEach(_ body: (CGPathElement) throws -> Swift.Void) rethrows

Note: A wrapper that provides a more Swift-friendly API can be defined by a Swift user like this:

extension CGPath {
    /// Call the given closure on each element of the path.
    func forEach(_ body: @escaping (CGPathElement) -> Void) {
        var info = body
        self.apply(info: &info) { (infoPtr, elementPtr) in
            let opaquePtr = OpaquePointer(infoPtr!)
            let body = UnsafeMutablePointer<(CGPathElement) -> Void>(opaquePtr).pointee
            body(elementPtr.pointee)
        }
    }
}

However, it would be preferable to be able to declare the closure non-escaping, and implementation within Core Graphics would probably provide better performance than a wrapper.


Steps to Reproduce:
N/A

Expected Results:
N/A

Actual Results:
N/A

Version:
Xcode Version 8.2.1 (8C1002)