Swift numerics and CGFloat (CGPoint, CGRect, etc.)

ios, swift

Solution

I wrote a library that handles operator overloading to allow interaction between Int, CGFloat and Double.

https://github.com/seivan/ScalarArithmetic

As of Beta 5, here's a list of things that you currently can't do with vanilla Swift. https://github.com/seivan/ScalarArithmetic#sample

I suggest running the test suite with and without ScalarArithmetic just to see what's going on.

Problem

I'm finding Swift numerics particularly clumsy when, as so often happens in real life, I have to communicate with Cocoa Touch with regard to CGRect and CGPoint (e.g., because we're talking about something's `frame` or `bounds`). CGFloat vs. Double Consider the following innocent-looking code from a UIViewController subclass: ``` let scale = 2.0 let r = self.view.bounds var r2 = CGRect() r2.size.width = r.size.width * scale ``` This code fails to compile, with the usual mysterious error on the last line: Could not find an overload for '*' that accepts the supplied arguments This error, as I'm sure you know by now, indicates some kind of impedance mismatch between types. `r.size.width` arrives as a CGFloat, which will interchange automatically with a Swift Float but cannot interoperate with a Swift Double variable (which, by default, is what `scale` is). The example is artificially brief, so there's an artificially simple solution, which is to cast `scale` to a Float from the get-go. But when many variables drawn from all over the place are involved in the calculation of a proposed CGRect's elements, there's a lot of casting to do. Verbose Initializer Another irritation is what happens when the time comes to create a new CGRect. Despite the documentation, there's no initializer with values but without labels. This fails to compile because we've got Doubles: ``` let d = 2.0 var r3 = CGRect(d, d, d, d) ``` But even if we cast `d` to a Float, we don't compile: Missing argument labels 'x:y:width:height:' in call So we end up falling back on `CGRectMake`, which is no improvement on Objective-C. And sometimes CGRectMake and CGSizeMake are no improvement. Consider this actual code from one of my apps: ``` let kSEP : Float = 2.0 let intercellSpacing = CGSizeMake(kSEP, kSEP); ``` In one of my projects, that works. In another, it mysteriously fails — the exact same code! — with this error: 'NSNumber' is not a subtype of 'CGFloat' It's as if, sometimes, Swift tries to "cross the bridge" by casting a Float to an NSNumber, which of course is the wrong thing to do when what's on the other side of the bridge expects a CGFloat. I have not yet figured out what the difference is between the two projects that causes the error to appear in one but not the other (perhaps someone else has). NOTE: I may have figured out that problem: it seems to depend on the Build Active Architecture Only build setting, which in turn suggests that it's a 64-bit issue. Which makes sense, since Float would not be a match for CGFloat on a 64-bit device. That means that the impedance mismatch problem is even worse than I thought. Conclusion I'm looking for practical words of wisdom on this topic. I'm thinking someone may have devised some CGRect and CGPoint extension that will make life a lot easier. (Or possibly someone has written a boatload of additional arithmetic operator function overloads, such that combining CGFloat with Int or Double "just works" — if that's possible.)

Original source

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