Apple libraries (CoreGraphics) seem to separate declaration and definition (Swift)

Question

According to the following similar question, it's impossible to separate function declarations and definitions.

Separation of function declaration and definition in Swift

However, I was trying to look at the implementation of CGRect and found the following in CoreGraphics/CGGeometry (by right-clicking on "CGRect" in my code and selecting "Jump to Definition").

struct CGRect {
var origin: CGPoint
var size: CGSize
}

extension CGRect {
static var zeroRect: CGRect { get }
static var nullRect: CGRect { get }
static var infiniteRect: CGRect { get }
init()
init(x: CGFloat, y: CGFloat, width: CGFloat, height: CGFloat)
init(x: Double, y: Double, width: Double, height: Double)
init(x: Int, y: Int, width: Int, height: Int)
var width: CGFloat { get }
var height: CGFloat { get }
var minX: CGFloat { get }
var midX: CGFloat { get }
var maxX: CGFloat { get }
var minY: CGFloat { get }
var midY: CGFloat { get }
var maxY: CGFloat { get }
var isNull: Bool { get }
var isEmpty: Bool { get }
var isInfinite: Bool { get }
var standardizedRect: CGRect { get }
mutating func standardize()
var integerRect: CGRect { get }
mutating func integerize()
func rectByInsetting(#dx: CGFloat, dy: CGFloat) -> CGRect
mutating func inset(#dx: CGFloat, dy: CGFloat)
func rectByOffsetting(#dx: CGFloat, dy: CGFloat) -> CGRect
mutating func offset(#dx: CGFloat, dy: CGFloat)
func rectByUnion(withRect: CGRect) -> CGRect
mutating func union(withRect: CGRect)
func rectByIntersecting(withRect: CGRect) -> CGRect
mutating func intersect(withRect: CGRect)
func rectsByDividing(atDistance: CGFloat, fromEdge: CGRectEdge) -> (slice: CGRect, remainder: CGRect)
func contains(rect: CGRect) -> Bool
func contains(point: CGPoint) -> Bool
func intersects(rect: CGRect) -> Bool
}

Did Apple manage to separate the definitions into a different file? Is there a way to find it if I want to see the actual implementation of CGRect?

Answer 1

Apple separated these using special Apple-only tools. You can't recreate this.

The entire implementation of CGRect is in CoreGraphics/CGGeometry.h:

struct CGRect {
  CGPoint origin;
  CGSize size;
};
typedef struct CGRect CGRect;

This is the ObjC equivalent to what the tools converted to Swift (or possibly someone hand coded, since these don't look like many of the other auto-generated Swift code):

struct CGRect {
  var origin: CGPoint
  var size: CGSize
}

If you mean how the various functions are implemented (like CGRectMake), no, those aren't available. I don't believe CoreGraphics is open source.