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