Minhao Dong - 1 year ago 35

Swift Question

I wrote an extension to CGRect class. I added a method which scales the CGRect by a factor. However i don't know how to write it so that I could achieve something like

`let newFrame = view.frame.scale(by: 0.8)`

and it returns a CGRect to be set to newFrame.

What I have tried so far..

`func scale(_ input: CGRect, byFactor factor: CGFloat) -> CGRect {`

let newCentre = input.centre

let newHeight = input.size.height * factor

let newWidth = input.size.width * factor

let newSize = CGSize(width: newWidth, height: newHeight)

let newRect = CGRect(centre: newCentre, size: newSize)

return newRect

}

Any help is appreciated. Thank you!

Edit:

`var upperLeft: CGPoint { return CGPoint(x: minX, y: minY) }`

var centre: CGPoint { return CGPoint(x: upperLeft.x + size.width/2, y: upperLeft.y + size.height/2) }

init(centre: CGPoint, size: CGSize) {

let upperLeft = CGPoint(x: centre.x-size.width/2, y: centre.y-size.height/2)

self.init(origin: upperLeft, size: size)

}

What I implemented in the extension

Answer Source

The receiver in an extension of a class, struct or enum is represented by `self`

```
extension CGRect {
func scale(byFactor factor: CGFloat) -> CGRect {
let newCentre = self.centre
let newHeight = self.height * factor // CGRect has width and height properties
let newWidth = self.width * factor
let newSize = CGSize(width: newWidth, height: newHeight)
let newRect = CGRect(centre: newCentre, size: newSize)
return newRect
}
}
```

PS: A simpler implementation of `centre`

is

```
var centre : CGPoint {
return CGPoint(x:CGRectGetMidX(self), y:CGRectGetMidY(self))
}
```