Implemented the path::join() function which concatenates two Paths.

Author: Mandrenkov

src/h/path.h

@@ -31,6 +31,17 @@ namespace ctgl {
         template <typename T>
         constexpr auto dropPrefix(T, Path<>) noexcept;
 
+        // Concatenates the given Paths using the following tabular expression:
+        // +-----------------------+     +---------+
+        // | p1 == DNE             | --> | DNE     |
+        // +-----------+-----------+     +---------+
+        // | p1 != DNE | p2 == DNE | --> | DNE     |
+        // |           +-----------+     +---------+
+        // |           | p2 != DNE | --> | p1 + p2 |
+        // +-----------+-----------+     +---------+
+        template <typename... Ts, typename... Us>
+        constexpr auto join(Path<Ts...> p1, Path<Us...> p2) noexcept;
+
         // Chooses the "shorter" of the given Paths using the following tabular expression:
         // +--------------------------------------------------+     +----+
         // | p1 == DNE                                        | --> | p2 |
@@ -84,6 +95,15 @@ namespace ctgl {
             return Path<>{};
         }
 
+        template <typename... Ts, typename... Us>
+        constexpr auto join(Path<Ts...> p1, Path<Us...> p2) noexcept {
+            if constexpr (p1 == DNE || p2 == DNE) {
+                return DNE;
+            } else {
+                return p1 + p2;
+            }
+        }
+
         template <typename... Ts, typename... Us>
         constexpr auto shortest(Path<Ts...> p1, Path<Us...> p2) noexcept {
             if constexpr (p1 == DNE) {

src/test/path_test.cpp

@@ -55,6 +55,19 @@ TEST(PathTest, DropPrefix) {
     EXPECT_EQ(path::dropPrefix(N4{}, Path<E34, E41, E23>{}), (Path<E41, E23>{}));
 }
 
+// Unit tests for the ctgl::path::join() function.
+TEST(PathTest, Join) {
+    // DNE
+    EXPECT_EQ(path::join(path::DNE, path::DNE), path::DNE);
+    EXPECT_EQ(path::join(Path<E11>{}, path::DNE), path::DNE);
+    EXPECT_EQ(path::join(path::DNE, Path<E11>{}), path::DNE);
+
+    // Exists
+    EXPECT_EQ(path::join(Path<E12>{}, Path<E23>{}), (Path<E12, E23>{}));
+    EXPECT_EQ(path::join(Path<E12>{}, Path<E12>{}), (Path<E12, E12>{}));
+    EXPECT_EQ(path::join(Path<E12, E23>{}, Path<E32, E21>{}), (Path<E12, E23, E32, E21>{}));
+}
+
 // Unit tests for the ctgl::path::shortest() function.
 TEST(PathTest, Shortest) {
     // DNE