[Foundation] Measurement: Fix hashing

Author: lorentey

Darwin/Foundation-swiftoverlay-Tests/TestMeasurement.swift

@@ -41,17 +41,17 @@ class MyDimensionalUnit : Dimension {
 }
 
 @available(OSX 10.12, iOS 10.0, watchOS 3.0, tvOS 10.0, *)
-class BugUnit : Unit {
+class CustomUnit : Unit {
     override init(symbol: String) {
-        precondition(symbol == "bug")
         super.init(symbol: symbol)
     }
 
     required init?(coder aDecoder: NSCoder) {
         super.init(coder: aDecoder)
     }
 
-    public static let bugs = BugUnit(symbol: "bug")
+    public static let bugs = CustomUnit(symbol: "bug")
+    public static let features = CustomUnit(symbol: "feature")
 }
 
 @available(OSX 10.12, iOS 10.0, watchOS 3.0, tvOS 10.0, *)
@@ -66,9 +66,9 @@ class TestMeasurement : TestMeasurementSuper {
         expectEqual(6, m3.value)
         expectEqual(m1, m2)
 
-        let m10 = Measurement(value: 2, unit: BugUnit.bugs)
-        let m11 = Measurement(value: 2, unit: BugUnit.bugs)
-        let m12 = Measurement(value: 3, unit: BugUnit.bugs)
+        let m10 = Measurement(value: 2, unit: CustomUnit.bugs)
+        let m11 = Measurement(value: 2, unit: CustomUnit.bugs)
+        let m12 = Measurement(value: 3, unit: CustomUnit.bugs)
 
         expectEqual(m10, m11)
         expectNotEqual(m10, m12)
@@ -89,7 +89,7 @@ class TestMeasurement : TestMeasurementSuper {
 
         // This correctly fails to build
 
-        // let m2 = Measurement(value: 1, unit: BugUnit.bugs)
+        // let m2 = Measurement(value: 1, unit: CustomUnit.bugs)
         // m2.converted(to: MyDimensionalUnit.unitKiloA)
     }
 
@@ -113,9 +113,9 @@ class TestMeasurement : TestMeasurementSuper {
         // Dynamically different dimensions
         expectEqual(Measurement(value: 1_001_000, unit: MyDimensionalUnit.unitA), oneMegaA + oneKiloA)
 
-        var bugCount = Measurement(value: 1, unit: BugUnit.bugs)
+        var bugCount = Measurement(value: 1, unit: CustomUnit.bugs)
         expectEqual(bugCount.value, 1)
-        bugCount = bugCount + Measurement(value: 4, unit: BugUnit.bugs)
+        bugCount = bugCount + Measurement(value: 4, unit: CustomUnit.bugs)
         expectEqual(bugCount.value, 5)
     }
 
@@ -154,6 +154,51 @@ class TestMeasurement : TestMeasurementSuper {
         expectTrue(fiveKM <= fiveThousandM)
     }
 
+    func testHashing() {
+        let lengths: [[Measurement<UnitLength>]] = [
+            [
+                Measurement(value: 5, unit: UnitLength.kilometers),
+                Measurement(value: 5000, unit: UnitLength.meters),
+                Measurement(value: 5000, unit: UnitLength.meters),
+            ],
+            [
+                Measurement(value: 1, unit: UnitLength.kilometers),
+                Measurement(value: 1000, unit: UnitLength.meters),
+            ],
+            [
+                Measurement(value: 1, unit: UnitLength.meters),
+                Measurement(value: 1000, unit: UnitLength.millimeters),
+            ],
+        ]
+        checkHashableGroups(lengths)
+
+        let durations: [[Measurement<UnitDuration>]] = [
+            [
+                Measurement(value: 3600, unit: UnitDuration.seconds),
+                Measurement(value: 60, unit: UnitDuration.minutes),
+                Measurement(value: 1, unit: UnitDuration.hours),
+            ],
+            [
+                Measurement(value: 1800, unit: UnitDuration.seconds),
+                Measurement(value: 30, unit: UnitDuration.minutes),
+                Measurement(value: 0.5, unit: UnitDuration.hours),
+            ]
+        ]
+        checkHashableGroups(durations)
+
+        let custom: [Measurement<CustomUnit>] = [
+            Measurement(value: 1, unit: CustomUnit.bugs),
+            Measurement(value: 2, unit: CustomUnit.bugs),
+            Measurement(value: 3, unit: CustomUnit.bugs),
+            Measurement(value: 4, unit: CustomUnit.bugs),
+            Measurement(value: 1, unit: CustomUnit.features),
+            Measurement(value: 2, unit: CustomUnit.features),
+            Measurement(value: 3, unit: CustomUnit.features),
+            Measurement(value: 4, unit: CustomUnit.features),
+        ]
+        checkHashable(custom, equalityOracle: { $0 == $1 })
+    }
+
     func test_AnyHashableContainingMeasurement() {
         let values: [Measurement<UnitLength>] = [
           Measurement(value: 100, unit: UnitLength.meters),
@@ -193,6 +238,7 @@ if #available(OSX 10.12, iOS 10.0, tvOS 10.0, watchOS 3.0, *) {
     MeasurementTests.test("testMeasurementFormatter") { TestMeasurement().testMeasurementFormatter() }
     MeasurementTests.test("testEquality") { TestMeasurement().testEquality() }
     MeasurementTests.test("testComparison") { TestMeasurement().testComparison() }
+    MeasurementTests.test("testHashing") { TestMeasurement().testHashing() }
     MeasurementTests.test("test_AnyHashableContainingMeasurement") { TestMeasurement().test_AnyHashableContainingMeasurement() }
   MeasurementTests.test("test_AnyHashableCreatedFromNSMeasurement") { TestMeasurement().test_AnyHashableCreatedFromNSMeasurement() }
     runAllTests()

Darwin/Foundation-swiftoverlay/Measurement.swift

@@ -36,8 +36,19 @@ public struct Measurement<UnitType : Unit> : ReferenceConvertible, Comparable, E
         self.unit = unit
     }
 
-    public var hashValue: Int {
-        return Int(bitPattern: __CFHashDouble(value))
+    public func hash(into hasher: inout Hasher) {
+        // Warning: The canonicalization performed here needs to be kept in
+        // perfect sync with the definition of == below. The floating point
+        // values that are compared there must match exactly with the values fed
+        // to the hasher here, or hashing would break.
+        if let dimension = unit as? Dimension {
+            // We don't need to feed the base unit to the hasher here; all
+            // dimensional measurements of the same type share the same unit.
+            hasher.combine(dimension.converter.baseUnitValue(fromValue: value))
+        } else {
+            hasher.combine(unit)
+            hasher.combine(value)
+        }
     }
 }
 
@@ -170,6 +181,10 @@ extension Measurement {
     /// If `lhs.unit == rhs.unit`, returns `lhs.value == rhs.value`. Otherwise, converts `rhs` to the same unit as `lhs` and then compares the resulting values.
     /// - returns: `true` if the measurements are equal.
     public static func ==<LeftHandSideType, RightHandSideType>(lhs: Measurement<LeftHandSideType>, rhs: Measurement<RightHandSideType>) -> Bool {
+        // Warning: This defines an equivalence relation that needs to be kept
+        // in perfect sync with the hash(into:) definition above. The floating
+        // point values that are fed to the hasher there must match exactly with
+        // the values compared here, or hashing would break.
         if lhs.unit == rhs.unit {
             return lhs.value == rhs.value
         } else {