How do you alloc/dealloc unsafe pointers in Swift?

Question

With Beta 4, I had this code that worked fine:

var red, green, blue, alpha: UnsafePointer
red = UnsafePointer.alloc(1)
green = Unsa         


        

Answer 1

To answer your question about setting the stroke color from a UIColor, this will work:

CGContextSetStrokeColorWithColor(myUIColor.CGColor);

I do this a lot in my C++-based Quartz 2D code.

Answer 2

This works, Swift is smart enough to know what to do with the & operator:

let color = UIColor.purpleColor()
var r:CGFloat, g:CGFloat, b:CGFloat, a:CGFloat = 0
color.getRed(&r, green: &g, blue: &b, alpha: &a)
CGContextSetRGBStrokeColor(c, r, g, b, a)

If you really want to do the alloc yourself, use your favorite flavor and construct the pointer like this:

let p = UnsafeMutablePointer<CGFloat>(calloc(1, UInt(sizeof(CGFloat))))
// later don't forget to free(p)

Answer 3

As of Beta 5 you can just pass your variables prefixed with &. Just make sure to initialise them

More info on https://developer.apple.com/swift/blog/?id=6

To use single variables, you can just set them to a zero value

var r: CGFloat = 0, g: CGFloat = 0, b: CGFloat = 0, a: CGFloat = 0
color.getRed(&r, green: &g, blue: &b, alpha: &a)

To use C arrays, you just create a normal array with the indices you expect

var points:[NSPoint] = [NSPoint(), NSPoint(), NSPoint()] //notice how we set empty NSPoints
self.elementAtIndex(index, associatedPoints: &points)
CGPathAddCurveToPoint(path, nil, points[0].x, points[0].y, points[1].x, points[1].y, points[2].x, points[2].y)

Answer 4

UnsafePointer<T> no longer has a member .alloc. Use UnsafeMutablePointer<T>.alloc instead. e.g. the following blankof() works as a universal initializer.

func blankof<T>(type:T.Type) -> T {
    var ptr = UnsafeMutablePointer<T>.alloc(sizeof(T))
    var val = ptr.memory
    ptr.destroy()
    return val
}

var red   = blankof(CGFloat)
var green = blankof(CGFloat)
var blue  = blankof(CGFloat)
var alpha = blankof(CGFloat)
color.getRed(&red, green:&green, blue:&blue, alpha:&alpha)
CGContextSetRGBStrokeColor(context, red, green, blue, 1)
// no need to dealloc because they are all structs, not pointers