(String) Add split support for multi-character delimiters (#5)

`split` support for multi-character delimiters:
```c++
split("a b->c***d", " ", "->", "***");    // {"a", "b", "c", "d"}
```

To support multi-character delimiters, the delimiters must now be
`string` or `string_view` and not `char`.

examples/StringExample.cpp

@@ -28,14 +28,14 @@ auto main() -> int
     // a b c
 
     // Split comma separated
-    for (const auto& s : split("a,b,c", ',')) {
+    for (const auto& s : split("a,b,c", ",")) {
         std::cout << s << " ";
     }
     std::cout << "\n";
     // a b c
 
     // Split multiple delimiters
-    for (const auto& s : split("a+b-c", '+', '-')) {
+    for (const auto& s : split("a+b-c", "+", "-")) {
         std::cout << s << " ";
     }
     std::cout << "\n";

include/educelab/core/utils/String.hpp

@@ -150,40 +150,63 @@ static auto trim_copy(const std::string_view s) -> std::string
     return std::string{trim(s)};
 }
 
-/** @brief Split a string by a delimiter */
+/**
+ * @brief Split a string by a delimiter
+ *
+ * When provided conflicting delimiters, the largest delimiter will take
+ * precedence:
+ *
+ * ```{.cpp}
+ * split("a->b->c", "-", "->");  // returns {"a", "b", "c"}
+ * ```
+ */
 template <typename... Ds>
 static auto split(std::string_view s, const Ds&... ds)
     -> std::vector<std::string_view>
 {
+    constexpr std::string_view DEFAULT_DELIM{" "};
+
     // Build delimiters list
-    std::vector<char> delimiters;
+    std::vector<std::string_view> delimiters;
     if (sizeof...(ds) > 0) {
         delimiters = {ds...};
     } else {
-        delimiters.emplace_back(' ');
+        delimiters.emplace_back(DEFAULT_DELIM);
     }
 
-    // Get a list of all delimiter start positions
-    std::vector<std::string_view::size_type> delimPos;
+    // Get a list of all delimiter start pos and sizes
+    std::vector<
+        std::pair<std::string_view::size_type, std::string_view::size_type>>
+        delimPos;
     for (const auto& delim : delimiters) {
         auto b = s.find(delim, 0);
         while (b != std::string_view::npos) {
-            delimPos.emplace_back(b);
-            b = s.find(delim, b + 1);
+            delimPos.emplace_back(b, delim.size());
+            b = s.find(delim, b + delim.size());
         }
     }
 
-    // Sort the delimiter start positions
-    std::sort(delimPos.begin(), delimPos.end());
+    // Sort the delimiter start positions by first and largest
+    std::sort(
+        delimPos.begin(), delimPos.end(),
+        [](const auto& l, const auto& r) { return l.second > r.second; });
+    std::sort(
+        delimPos.begin(), delimPos.end(),
+        [](const auto& l, const auto& r) { return l.first < r.first; });
 
     // Split string
     std::vector<std::string_view> tokens;
     std::string_view::size_type begin{0};
-    for (const auto end : delimPos) {
+    for (const auto [end, size] : delimPos) {
+        // ignore nested delimiters
+        if (end < begin) {
+            continue;
+        }
+        // get from begin to delim start
         if (auto t = s.substr(begin, end - begin); not t.empty()) {
             tokens.emplace_back(t);
         }
-        begin = end + 1;
+        begin = end + size;
     }
     if (auto t = s.substr(begin); not t.empty()) {
         tokens.emplace_back(t);

tests/src/TestString.cpp

@@ -139,13 +139,23 @@ TEST(String, Split)
     EXPECT_EQ(split("  a  b  c  "), expected);
 
     // Space separated (explicit)
-    EXPECT_EQ(split("a b c", ' '), expected);
+    EXPECT_EQ(split("a b c", " "), expected);
 
     // Comma separated
-    EXPECT_EQ(split("a,b,c", ','), expected);
+    EXPECT_EQ(split("a,b,c", ","), expected);
 
     // Multi-delimited
-    EXPECT_EQ(split("a+b-c", '+', '-'), expected);
+    EXPECT_EQ(split("a+b-c", "+", "-"), expected);
+
+    // Multi-character delimiter
+    EXPECT_EQ(split("a b->c", " ", "->"), expected);
+
+    // Multi-character, ignore nested
+    EXPECT_EQ(split("a-b->c", "-", "->"), expected);
+
+    // Overlapping will only consume first delim
+    expected = {"a", "b", ">c"};
+    EXPECT_EQ(split("a--b-->c", "--", "->"), expected);
 
     // Sentence
     expected = {"This", "is", "only", "a", "test."};