wip

Author: ollieatkinson

Sources/Algorithms/Stride.swift

@@ -103,9 +103,9 @@ extension Stride: Collection {
   }
 
   public func index(_ i: Index, offsetBy distance: Int) -> Index {
-    precondition(i.base < base.endIndex, "Advancing past end index")
-    let limit = distance > 0 ? endIndex : startIndex
-    return index(i, offsetBy: distance, limitedBy: limit) ?? limit
+    precondition(distance <= 0 || i.base < base.endIndex, "Advancing past end index")
+    precondition(distance >= 0 || i.base > base.startIndex, "Incrementing past start index")
+    return Index(base.index(i.base, offsetBy: distance * stride))
   }
 }
 

Tests/SwiftAlgorithmsTests/StrideTests.swift

@@ -88,8 +88,16 @@ final class StridingTests: XCTestCase {
     XCTAssertEqual(a.striding(by: 11).count, [0].count)
   }
 
+  func testIndexTraversals() {
+    validateIndexTraversals(
+      (0...100).striding(by: 10)
+//      (0...100).striding(by: 11)
+//      (0...100).striding(by: 101)
+    )
+  }
+  
   func testDistance() {
-    
+
     do {
       let a = (0...100).striding(by: 11)
       XCTAssertEqual(a.distance(from: a.startIndex, to: a.endIndex), a.count)
@@ -128,7 +136,7 @@ final class StridingTests: XCTestCase {
       }
 
       var i = a.startIndex
-      a.formIndex(&i, offsetBy: 3)
+      a.formIndex(&i, offsetBy: 1)
       XCTAssertEqual(a.distance(from: a.startIndex, to: i), a.count)
       XCTAssertEqual(i, a.endIndex)
 //      a[i] // == Fatal error: Index out of range