Add CustomStringConvertible conformances to Pair types (#204)

Sources/DataStructures/Pair/Cross.swift

@@ -41,3 +41,13 @@ extension Cross: Comparable where T: Comparable, U: Comparable {
 
 extension Cross: Equatable where T: Equatable, U: Equatable { }
 extension Cross: Hashable where T: Hashable, U: Hashable { }
+
+extension Cross: CustomStringConvertible {
+
+    // MARK: - CustomStringConvertible
+
+    /// Printable description of `Cross`.
+    public var description: String {
+        return "<\(a),\(b)>"
+    }
+}

Sources/DataStructures/Pair/OrderedPair.swift

@@ -28,3 +28,13 @@ public struct OrderedPair <T>: SwappablePair {
 
 extension OrderedPair: Equatable where T: Equatable { }
 extension OrderedPair: Hashable where T: Hashable { }
+
+extension OrderedPair: CustomStringConvertible {
+
+    // MARK: - CustomStringConvertible
+
+    /// Printable description of `OrderedPair`.
+    public var description: String {
+        return "(\(a),\(b))"
+    }
+}

Sources/DataStructures/Pair/UnorderedPair.swift

@@ -58,3 +58,13 @@ extension UnorderedPair: Hashable where T: Hashable {
         hasher.combine(a.hashValue ^ b.hashValue)
     }
 }
+
+extension UnorderedPair: CustomStringConvertible {
+
+    // MARK: - CustomStringConvertible
+
+    /// Printable description of `UnorderedPair`.
+    public var description: String {
+        return "{\(a),\(b)}"
+    }
+}

Tests/DataStructuresTests/CrossTests.swift

@@ -39,4 +39,8 @@ class CrossTests: XCTestCase {
         }
         XCTAssertEqual(start.map(function),expected)
     }
+
+    func testDescription() {
+        XCTAssertEqual(Cross("a",0).description, "<a,0>")
+    }
 }

Tests/DataStructuresTests/PairTests/OrderedPairTests.swift

@@ -15,4 +15,8 @@ class OrderedPairTests: XCTestCase {
         let expected = OrderedPair(1,2)
         XCTAssertEqual(start.map { $0.count }, expected)
     }
+
+    func testDescription() {
+        XCTAssertEqual(OrderedPair("3","four").description, "(3,four)")
+    }
 }

Tests/DataStructuresTests/PairTests/UnorderedPairTests.swift

@@ -64,6 +64,10 @@ class UnorderedPairTests: XCTestCase {
         let expected = UnorderedPair(1,2)
         XCTAssertEqual(start.map { $0.count }, expected)
     }
+
+    func testDescription() {
+        XCTAssertEqual(UnorderedPair("a","z").description, "{a,z}")
+    }
 }
 
 func randomString(maxLength: Int = 10) -> String {

Tests/DataStructuresTests/XCTestManifests.swift

@@ -110,6 +110,7 @@ extension CrossTests {
         ("testComparableFalseEqual", testComparableFalseEqual),
         ("testComparableLexicographic", testComparableLexicographic),
         ("testComparableLexicographicFalse", testComparableLexicographicFalse),
+        ("testDescription", testDescription),
         ("testMap", testMap),
     ]
 }
@@ -285,6 +286,7 @@ extension OrderedDictionaryTests {
 
 extension OrderedPairTests {
     static let __allTests = [
+        ("testDescription", testDescription),
         ("testMap", testMap),
     ]
 }
@@ -518,6 +520,7 @@ extension TreeTests {
 
 extension UnorderedPairTests {
     static let __allTests = [
+        ("testDescription", testDescription),
         ("testEquatable", testEquatable),
         ("testHashValuesInt", testHashValuesInt),
         ("testHashValuesString", testHashValuesString),