The document discusses new features in iOS 10 for working with measurements and units, including the Measurement struct for representing values with units, Dimension classes for defining units of measurement, and the MeasurementFormatter class for formatting measurements based on locale. Key points covered include how to perform calculations with measurements, define custom units and dimensions, and get locale-aware string representations of measurements.

1. Measurements & Units
WWDC16. Meetup@Wantedly
2016/06/30

2. About me
Ken Tominaga
The University of Tokyo
Rekimoto Lab
Swift Lover 😍

3. Measurements
and
Units? 😳

4. Nike+ Running

5. Measurements and Units
Added to the Foundation framework
Newly introduced in iOS 10
Support for specifying Measurements and Units

6. Measurement
public struct Measurement<UnitType : Unit> : Comparable, Equatable {
public let unit: UnitType
public var value: Double
public init(value: Double, unit: UnitType)
}

7. Calculations With
Measurements
let distanceTraveled = Measurement(value: 20, unit: UnitLength.kilometers)
// 20.0 km
let distanceToGo = Measurement(value: 1.975, unit: UnitLength.kilometers)
// 1.975 km
let totalDistance = distanceTraveled + distanceToGo // 21.975 km
let tripleDistance = 3 * distanceToGo // 5.925 km
let halfDistance = distanceToGo / 2 // 0.9875 km

8. Properties of a Unit
Symbol “m"
Dimension “meter is a unit of length"
Equivalence 1 m = 3.28084 ft

9. Unit
public class Unit : NSObject, NSCopying {
public var symbol: String { get }
public init(symbol: String)
}

10. Dimension
Categories of units
Expressed with different units
• Length: km, m, ft, mi, etc.
Always has a base unit
let meter = UnitLength.baseUnit()
Can perform conversions
• km ft, m mi

11. Dimension
public class Dimension : Unit {
@NSCopying public var converter: UnitConverter { get }
public init(symbol: String, converter: UnitConverter)
public class func baseUnit() -> Self
}

12. Dimension
Instances as units
Singletons for most common units
International System of Units
public class UnitLength : Dimension {
/*
Base unit - meters
*/
@NSCopying public class var kilometers: UnitLength { get }
@NSCopying public class var meters: UnitLength { get }
@NSCopying public class var feet: UnitLength { get }
@NSCopying public class var yards: UnitLength { get }
@NSCopying public class var miles: UnitLength { get }
...
}

13. Dimension

14. Implicit Conversion
let distanceTraveled = Measurement(value: 2, unit: UnitLength.kilometers)
// 2.0 km
//let distanceToGo = Measurement(value: 1.975, unit: UnitLength.kilometers)
//let totalDistance = distanceTraveled + distanceToGo
let distanceToGo = Measurement(value: 11.3, unit: UnitLength.feet)
// 11.3 ft
let totalDistance = distanceTraveled + distanceToGo
// 2003.44424 m

15. Next Step

16. Custom Unit
let syaku =
UnitLength(symbol: " ", converter: UnitConverterLinear(coefficient: 10/33))
// 1 10/30 m

17. Conversion
baseUnit unit
UnitConverter
• baseUnitValue(fromValue value:)
• value(fromBaseUnitValue baseUnitValue:)
UnitConverterLinear
• baseUnitValue = coefficient * value + constant
• value = (baseUnitValue - constant)/coefficient

18. Custom Unit
let syaku =
UnitLength(symbol: " ", converter: UnitConverterLinear(coefficient: 10/33))
// 1 10/33 m
let lengthInShayku = Measurement(value: 10, unit: syaku)
// 10.0
let lengthInYards = lengthInShayku.converted(to: UnitLength.yards)
// 3.31397969193245 yd
let lengthInFeet = Measurement(value: 5.3, unit: UnitLength.feet)
// 5.3 ft
lengthInShayku + lengthInFeet
// 4.64574303030303 m
baseUnitValue = 10/ 33 *
= baseUnitValue / (10/33)

19. Custom Dimension
class UnitImpression : Dimension {
static let good =
UnitImpression(symbol: "👍 ", converter: UnitConverterLinear(coefficient: 1))
static let great =
UnitImpression(symbol: "👏 ", converter: UnitConverterLinear(coefficient: 10))
static let wonderful =
UnitImpression(symbol: "😘 ", converter: UnitConverterLinear(coefficient: 50))
static let lifeChanging =
UnitImpression(symbol: "😍 ", converter: UnitConverterLinear(coefficient: 2000))
override class func baseUnit() -> UnitImpression {
return good
}
}

20. // Example - Use of Custom Dimension
struct Presentation {
let speaker : String
let title : String
let movement : Measurement<UnitLength>
let duration : Measurement<UnitDuration>
let impression : Measurement<UnitImpression>
var movementRate: Measurement<UnitSpeed> {
let distanceInMeters = movement.converted(to: .meters)
let durationInSeconds = duration.converted(to: .seconds)
return Measurement(
value: distanceInMeters.value / durationInSeconds.value,
unit: UnitSpeed.metersPerSecond)
}
}

21. // Example - Use of Custom Dimension
let presentation =
Presentation(
speaker: "ken0nek",
title: "Measurements & Units",
movement: Measurement(value: 60, unit: UnitLength.centimeters),
duration: Measurement(value: 10, unit: UnitDuration.minutes),
impression: Measurement(value: 100, unit: UnitImpression.lifeChanging))
presentation.movementRate // 0.001 m/s
presentation.impression // 100.0 😍
presentation.impression.converted(to: UnitImpression.baseUnit()) // 200000.0 👍

22. Formatting Is Hard
Country Expected String
Japan “5 km"
United States “3.1 mi”
Egypt “‫كم‬ ٥”
China “5 "

23. MeasurementFormatter
New formatter
Measurements and Units
Locale-aware formatting

24. MeasurementFormatter
public class MeasurementFormatter : Formatter {
public var unitOptions: MeasurementFormatter.UnitOptions
public var unitStyle: Formatter.UnitStyle
@NSCopying public var locale: Locale!
@NSCopying public var numberFormatter: NumberFormatter!
public func string(from measurement: Measurement<Unit>) -> String
public func string(from unit: Unit) -> String
}

25. Unit Options
Formats preferred unit of locale by default
Takes purpose into account

26. Unit Options
UnitOptions Measurement Locale Example String
.providedUnit
value: 5,
unit: .kilometers
“en_US” “5 km"
.naturalScale
value: 1000,
unit: .meters
“fr_FR” “1 km"
.temperatureWithoutUnit
value: 90,
unit: .fahrenheit
“en_US” “90°"

27. MeasurementFormatter
// Current Locale -> ja_JP
// This code will not work in Xcode8 beta currently :(
let formatter = MeasurementFormatter()
let distance = Measurement(value: 5, unit: UnitLength.miles)
formatter.string(from: distance)
// 8.04672 km
let syaku = UnitLength(symbol: " ",
converter: UnitConverterLinear(coefficient: 10/33))
let syakuDistance = Measurement(value: 660, unit: syaku)
formatter.string(from: syakuDistance)
// 0.2 km

28. Wrap Up
Support for handling Measurements and Units
Don’t have to care about localizing and formatting
Measurement
Unit
Dimension MeasurementFormatter
UnitConverter

29. Thank you

30. References
Measurements and Units - WWDC 2016 - Videos - Apple
Developer
Measurement - Apple Developer Documentation
Unit - Apple Developer Documentation
Dimension - Apple Developer Documentation
UnitConverterLinear - Apple Developer Documentation
MeasurementFormatter - Apple Developer Documentation
About Internationalization and Localization

31. Bug Reports
The string() method of the
MeasurementFormatter... | Apple Developer
Forums
Swift Compiler on iOS 10 does not properly find
MeasurementFormatter.string(from:) method