NULL parameter in Swift - swift

Question

In Objective-C, we can declare a function like this:
- (void)getRect:(CGRect *)aRectRef bRect:(CGRect *)bRectRef
{
if (aRectRef) *aRectRef = CGRectZero
if (bRectRef) *bRectRef = CGRectZero
}
and pass NULL to the function:
CGRect rect;
[self getRect:NULL bRect:rect]
There isn't NULL in Swift. I can't use nil as inout param directly either:
func getRect(aRect aRectRef: inout CGRect?, bRect bRectRef: inout CGRect?) -> Void {
...
}
self.getRect(&nil, bRect: rect) // <- ERROR
I must define a variable with nil value and pass it to the function, even though I don't need the variable totally.
How to pass nil to the function?
UPDATE:
null / nil in swift language just explained nil in Swift.
Swift optional inout parameters and nil explained how to define a variable with nil value and pass it as inout parameter.
I want to know there is a way to pass nil directly like &nil to function or not.

Answer 1

Your Objective-C method has nullable pointers as parameters,
in Swift 3 that would be an optional UnsafeMutablePointer:
func getRect(aRectRef: UnsafeMutablePointer<CGRect>?, bRectRef: UnsafeMutablePointer<CGRect>?) {
if let aRectPtr = aRectRef {
aRectPtr.pointee = CGRect(x: 1, y: 2, width: 3, height: 4)
}
if let bRectPtr = bRectRef {
bRectPtr.pointee = CGRect(x: 5, y: 6, width: 7, height: 8)
}
}
var rect = CGRect.zero
getRect(aRectRef: &rect, bRectRef: nil)
print(rect) // (1.0, 2.0, 3.0, 4.0)
So you can pass nil as an argument. What you can not do
(in contrast to Objective-C) is to pass the address of an uninitialized variable, rect must be initialized here.
The same can be written more compactly as
func getRect(aRectRef: UnsafeMutablePointer<CGRect>?, bRectRef: UnsafeMutablePointer<CGRect>?) {
aRectRef.map { $0.pointee = CGRect(x: 1, y: 2, width: 3, height: 4) }
bRectRef.map { $0.pointee = CGRect(x: 5, y: 6, width: 7, height: 8) }
}

Answer 2

Sorry, I am not allowed to add comment at this time, so I'll write this as an answer. In SWIFT, you defined the parameter as inout, you have to pass in a variable and not literal nil. You can do something like this,
func testGetRect()
{
var recta: CGRect? = nil
var rectb: CGRect? = CGRect()
self.getRect(aRect: &recta, bRect: &rectb)
}
func getRect(inout aRect aRectRef: CGRect?, inout bRect bRectRef: CGRect?) -> Void
{
if (aRectRef != nil)
{
aRectRef = CGRectZero
}
if (bRectRef != nil)
{
bRectRef = CGRectZero
}
}
Yes, you "must define a variable with nil and pass it to the function. I tried some casting to see if it work, but couldn't. The parameter passing with inout is like C++ parameter passing by reference, i.e foo(int &parama, int &paramb). You must pass a variables to foo. I don't believe SWIFT has parameter passing like the obj-c example that you have.