UnsafePointer<CGAffineTransform> from CGAffineTransform

Question

I'm trying to create a CGPath in Swift. I'm using CGPathCreateWithRect(rect, transformPointer).

How can I get an UnsafePointer<CGAffineTransform> from a CGAffineTransform? I've tried this:

    let transform : CGAffineTransform = CGAffineTransformIdentity
    let transformPointer : UnsafePointer<CGAffineTransform> = UnsafePointer(transform)

I've also tried this:

    let transform : CGAffineTransform = CGAffineTransformIdentity
    let transformPointer : UnsafePointer<CGAffineTransform> = &transform 

but Swift complains about a '&' with non-inout argument of type.... I've also tried passing &transform directly into CGPathCreateWithRect but that stops with same error.

When I pass in transform directly, Swift "Cannot convert value of type 'CGAffineTransform' to expected argument type 'UnsafePointer'".

What's going on, and how can make this work with Swift 2.1?

Answer 1

I've also tried passing &transform directly into CGPathCreateWithRect ...

You were almost there. transform needs to be a variable in order to pass it as an inout argument with &:

var transform = CGAffineTransformIdentity
let path = CGPathCreateWithRect(CGRect(...), &transform)

For more information, see "Interacting with C APIs" in the "Using Swift with Cocoa and Objective-C" documentation.

---

In Swift 3 this would be

var transform = CGAffineTransform.identity
let path = CGPath(rect: rect, transform: &transform)

or, for the identity transform, just

let path = CGPath(rect: rect, transform: nil)

Answer 2

@Martin R provides the best answer, but as an alternative, I like to use my unsafe mutable pointers this way, in case you need to alter the actual pointer in the future

let path = withUnsafeMutablePointer(&transform)
{
  CGPathCreateWithRect(CGRect(...), UnsafeMutablePointer($0))
}