Merge pull request #2 from LucianoPAlmeida/cost-option

Improvements on cost model API.

Sources/strings/Levenshtein.swift

@@ -5,10 +5,10 @@
 //
 //===----------------------------------------------------------------------===//
 
-public struct LevenshteinCost {
-  public let insertion: Int
-  public let deletion: Int
-  public let substitution: Int
+public struct LevenshteinCost: Equatable {
+  public var insertion: Int
+  public var deletion: Int
+  public var substitution: Int
 
   public init(insertion: Int = 1, deletion: Int = 1, substitution: Int = 1) {
     self.insertion = insertion
@@ -17,6 +17,30 @@ public struct LevenshteinCost {
   }
 
   public static var `default`: LevenshteinCost { LevenshteinCost() }
+
+  @inlinable
+  internal func _with(
+    _ property: WritableKeyPath<LevenshteinCost, Int>, value: Int
+  ) -> LevenshteinCost {
+    var copy = self
+    copy[keyPath: property] = value
+    return copy
+  }
+
+  @inlinable
+  public func with(insertion: Int) -> LevenshteinCost {
+    return _with(\.insertion, value: insertion)
+  }
+
+  @inlinable
+  public func with(deletion: Int) -> LevenshteinCost {
+    return _with(\.deletion, value: deletion)
+  }
+
+  @inlinable
+  public func with(substitution: Int) -> LevenshteinCost {
+    return _with(\.substitution, value: substitution)
+  }
 }
 
 public struct Levenshtein<Source: StringProtocol> {

Tests/stringsTests/LevenshteinTests.swift

@@ -28,6 +28,15 @@ final class LevenshteinTests: XCTestCase {
     XCTAssertEqual("friend".levenshteinDistance(to: "fried", cost: cost), 1)
     XCTAssertEqual("test".levenshteinDistance(to: "team", cost: cost), 4)
   }
+
+  func testLevenshteinCost() {
+    let cost = LevenshteinCost.default
+    let expected = LevenshteinCost(insertion: 3, deletion: 4, substitution: 5)
+
+    XCTAssertNotEqual(expected, cost)
+    XCTAssertEqual(expected, cost.with(deletion: 4).with(insertion: 3).with(substitution: 5))
+
+  }
 
   static var allTests = [
     ("testLevenshteinDistances", testLevenshteinDistances),