Merge pull request #3066 from xwu/decimal-distance

[SR-6785] Fix `Decimal` conformance to `Strideable`

Author: xwu

Darwin/Foundation-swiftoverlay-Tests/TestDecimal.swift

@@ -289,8 +289,6 @@ class TestDecimal : XCTestCase {
         XCTAssertEqual(Decimal(-9), Decimal(1) - Decimal(10))
         XCTAssertEqual(Decimal(3), Decimal(2).nextUp)
         XCTAssertEqual(Decimal(2), Decimal(3).nextDown)
-        XCTAssertEqual(Decimal(-476), Decimal(1024).distance(to: Decimal(1500)))
-        XCTAssertEqual(Decimal(68040), Decimal(386).advanced(by: Decimal(67654)))
         XCTAssertEqual(Decimal(1.234), abs(Decimal(1.234)))
         XCTAssertEqual(Decimal(1.234), abs(Decimal(-1.234)))
         if #available(macOS 10.15, iOS 13, tvOS 13, watchOS 6, *) {
@@ -597,6 +595,17 @@ class TestDecimal : XCTestCase {
             }
         }
     }
+
+    func test_Strideable() {
+        XCTAssertEqual(Decimal(476), Decimal(1024).distance(to: Decimal(1500)))
+        XCTAssertEqual(Decimal(68040), Decimal(386).advanced(by: Decimal(67654)))
+
+        let x = 42 as Decimal
+        XCTAssertEqual(x.distance(to: 43), 1)
+        XCTAssertEqual(x.advanced(by: 1), 43)
+        XCTAssertEqual(x.distance(to: 41), -1)
+        XCTAssertEqual(x.advanced(by: -1), 41)
+    }
 
     func test_ULP() {
         let x = 0.1 as Decimal

Darwin/Foundation-swiftoverlay/Decimal.swift

@@ -316,7 +316,7 @@ extension Decimal {
 
 extension Decimal : Strideable {
     public func distance(to other: Decimal) -> Decimal {
-        return self - other
+        return other - self
     }
 
     public func advanced(by n: Decimal) -> Decimal {

Sources/Foundation/Decimal.swift

@@ -485,7 +485,7 @@ extension Decimal {
 
 extension Decimal : Strideable {
     public func distance(to other: Decimal) -> Decimal {
-        return self - other
+        return other - self
     }
     public func advanced(by n: Decimal) -> Decimal {
         return self + n

Tests/Foundation/Tests/TestDecimal.swift

@@ -376,8 +376,6 @@ class TestDecimal: XCTestCase {
         XCTAssertEqual(Decimal(-9), Decimal(1) - Decimal(10))
         XCTAssertEqual(Decimal(3), Decimal(2).nextUp)
         XCTAssertEqual(Decimal(2), Decimal(3).nextDown)
-        XCTAssertEqual(Decimal(-476), Decimal(1024).distance(to: Decimal(1500)))
-        XCTAssertEqual(Decimal(68040), Decimal(386).advanced(by: Decimal(67654)))
         XCTAssertEqual(Decimal(1.234), abs(Decimal(1.234)))
         XCTAssertEqual(Decimal(1.234), abs(Decimal(-1.234)))
         XCTAssertEqual((0 as Decimal).magnitude, 0 as Decimal)
@@ -849,6 +847,17 @@ class TestDecimal: XCTestCase {
 
         XCTAssertEqual(100,number.objCType.pointee, "ObjC type for NSDecimalNumber is 'd'")
     }
+
+    func test_Strideable() {
+        XCTAssertEqual(Decimal(476), Decimal(1024).distance(to: Decimal(1500)))
+        XCTAssertEqual(Decimal(68040), Decimal(386).advanced(by: Decimal(67654)))
+
+        let x = 42 as Decimal
+        XCTAssertEqual(x.distance(to: 43), 1)
+        XCTAssertEqual(x.advanced(by: 1), 43)
+        XCTAssertEqual(x.distance(to: 41), -1)
+        XCTAssertEqual(x.advanced(by: -1), 41)
+    }
 
     func test_ULP() {
         let x = 0.1 as Decimal
@@ -1460,6 +1469,7 @@ class TestDecimal: XCTestCase {
             ("test_ScanDecimal", test_ScanDecimal),
             ("test_SimpleMultiplication", test_SimpleMultiplication),
             ("test_SmallerNumbers", test_SmallerNumbers),
+            ("test_Strideable", test_Strideable),
             ("test_ULP", test_ULP),
             ("test_ZeroPower", test_ZeroPower),
             ("test_parseDouble", test_parseDouble),