A ratio of two related quantities, expressed in terms of an amount of numerator unit per single denominator unit.
This functionality is discussed in Chapter 5 of Flight School Guide to Swift Numbers.
- Swift 4.0+
Swift Package Manager
Add the Rate package to your target dependencies in
import PackageDescription let package = Package( name: "YourProject", dependencies: [ .package( url: "https://github.com/Flight-School/Rate", from: "1.0.0" ), ] )
Then run the
swift build command to build your project.
To use Rate in your Xcode project using Carthage,
specify it in
github "Flight-School/Rate" ~> 1.0.0
Then run the
carthage update command to build the framework,
and drag the built Rate.framework into your Xcode project.
One of the shortcomings of the Foundation Unit and Measurement APIs is the inability to dynamically declare compound units. This can make it difficult to perform dimensional analysis and other multi-step calculations.
Rate structure allows you to express the ratio
between two units in a type-safe manner.
Multiplying a measurement with one unit type by a rate
whose denominator is that same unit type causes those types to cancel out,
resulting in a measurement with the numerator type.
For example, volume over time multiplied by time yields volume:
let flowRate = Rate<UnitVolume, UnitDuration>(value: 84760, unit: .cubicFeet, per: .seconds) let oneDay = Measurement<UnitDuration>(value: 24, unit: .hours) (flowRate * oneDay).converted(to: .megaliters) // 207371ML