Just tried pulling this into a new Xcode 11.1 project using the GUI SPM flow, and got this build error.

Adding

import CoreGraphics

at the top of Percent.swift fixed it for me. Happy to submit a PR if you want it!

Hey Sindre, this is a cool library! If I'm reading the source code correctly, suppose I had the following struct:

struct SomeObject: Codable {
    let alpha: Percent
}

That object would be encoded as below (and require the below JSON to decode):

{
    alpha: {
        rawValue: 10
    }
}

it may be a nice enhancement to override the default Encodable/Decodable implementations to parse that struct as:

{
    alpha: 0.1
}

I feel this is more likely what you'd get from an API. Up to you whether you want to keep the implementation as is, entirely change it to the above, or maybe provide some static variable to allow users to choose which Codable representation they want.

It would allow us to store bigger values with more precision. We would also accept a Decimal and add arithmetics overloads for it.

I don't intend to do this yet if at all as Decimal has and still is very buggy:

• JSONDecoder Decimal precision error
• Decimal initialized with Double loses precision

Even though I don't plan to do this yet, I'm still looking for feedback on whether it makes sense at all.

Prior to this change, calculating such percentage from values of types different than Double would require type casting boilerplate. Now it is possible to find percentage of any BinaryInteger or BinaryFloatingPoint, with result always matching the original input type. Having mixed input and output is also supported, meaning it is possible to obtain the percentage of BinaryInteger as BinaryFloatingPoint (although not vice-versa; using an explicit type casting seems more reasonable in such cases).

I am using this in an app and I thougt it might be useful to have it in the standard package.

Similar to Double.random(in:) (which it uses internally)

I would have added tests but I am not sure how to test something that is random by design 🤔

Not sure whether there are any downsides with doing that, but would be nice if Percentage could be used with generic numeric methods.

https://developer.apple.com/documentation/swift/numeric

Would be nice to be able to use this with Swift/Cocoa APIs that accept a fraction Double.

For example:

• https://developer.apple.com/documentation/uikit/uicolor/1621922-withalphacomponent
• https://developer.apple.com/documentation/appkit/nscolor/1526906-withalphacomponent
• https://developer.apple.com/documentation/swiftui/color/3049763-opacity
• https://developer.apple.com/documentation/swiftui/hstack/3269261-opacity
• https://developer.apple.com/documentation/swiftui/hstack/3269155-brightness
• https://developer.apple.com/documentation/swiftui/hstack/3269164-contrast
• https://developer.apple.com/documentation/swiftui/hstack/3269293-saturation
• https://developer.apple.com/documentation/swiftui/hstack/3269207-grayscale

Does this make sense?

Some ideas:

• .clampedZeroToHundred which clamps the percentage to 0...100.
• Percent.from(100, of: 200) //=> 50%
• Find the original value before a percent increase. E.g. If a value is 120 after a 40% increase, what is the original value before the increase?
• Find the original value before a percent decrease. E.g. If a value is 106 after a 12% decrease, what is the original value before the decrease?
• "x IS y% OF". E.g. 67 is 90% of what?

What else?