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+
Add the Rate package to your target dependencies in Package.swift
:
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 Cartfile
:
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.
The 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
MIT
Mattt (@mattt)