feat: add lazy split in string op namespace.

src/yycc/patch/stream.hpp

@@ -10,7 +10,8 @@
  */
 namespace yycc::patch::stream {
 
-    // TODO: replace all old way of outputing utf8 string with this new way.
+    // TODO: fix all REINTERPRET::as_ordinary_view polyfill for std::ostream.
+    // TODO: replace all old way (C-style output) with this new way if possible.
 
     std::ostream& operator<<(std::ostream& os, const std::u8string_view& u8str);
     std::ostream& operator<<(std::ostream& os, const char8_t* u8str);

src/yycc/string/op.cpp

@@ -168,45 +168,115 @@ namespace yycc::string::op {
 
 #pragma region Split
 
-    std::vector<std::u8string_view> split(const std::u8string_view& strl, const std::u8string_view& _delimiter) {
+    // Reference:
-        // Reference:
+    // https://stackoverflow.com/questions/14265581/parse-split-a-string-in-c-using-string-delimiter-standard-c
-        // https://stackoverflow.com/questions/14265581/parse-split-a-string-in-c-using-string-delimiter-standard-c
 
-        // prepare return value
+#pragma region Lazy Split Iterator
+
+    LazySplitIterator::LazySplitIterator(std::optional<std::u8string_view> strl, const std::u8string_view& delimiter) :
+        m_current_str(std::nullopt), m_next_str(strl), m_delimiter(delimiter) {
+        // We can archive result by assign string into next string,
+        // and call next operator.
+        ++(*this);
+    }
+
+    LazySplitIterator::reference LazySplitIterator::operator*() const {
+        return m_current_str.value();
+    }
+
+    LazySplitIterator::pointer LazySplitIterator::operator->() const {
+        return &m_current_str.value();
+    }
+
+    LazySplitIterator& LazySplitIterator::operator++() {
+        // move next string to current string and clear next string
+        m_current_str = m_next_str;
+        m_next_str = std::nullopt;
+
+        // check whether there is string to be spliited
+        if (m_current_str.has_value()) {
+            // extract string
+            const auto strl = m_current_str.value();
+
+            // if delimiter is empty, return original string.
+            // if string need to be splitted is empty, return original string (empty string).
+            if (strl.empty() || m_delimiter.empty()) {
+                m_current_str = strl;
+                m_next_str = std::nullopt;
+            } else {
+                // start spliting
+                size_t current = 0;
+                if ((current = strl.find(m_delimiter)) != std::u8string_view::npos) {
+                    // We still can find items, split it and put into 2 string view respectively.
+                    m_current_str = strl.substr(0, current);
+                    m_next_str = strl.substr(current + m_delimiter.size());
+                } else {
+                    // We can not find any more delimiter, so this is the last item
+                    m_current_str = strl;
+                    m_next_str = std::nullopt;
+                }
+            }
+        } else {
+            // No value. Initialize as an end iterator.
+            m_current_str = std::nullopt;
+            m_next_str = std::nullopt;
+        }
+
+        // return self
+        return *this;
+    }
+
+    LazySplitIterator LazySplitIterator::operator++(int) {
+        LazySplitIterator temp = *this;
+        ++(*this);
+        return temp;
+    }
+
+    bool LazySplitIterator::operator==(const LazySplitIterator& other) const {
+        return (this->m_current_str == other.m_current_str) && (this->m_next_str == other.m_next_str)
+               && (this->m_delimiter == other.m_delimiter);
+    }
+
+    bool LazySplitIterator::operator!=(const LazySplitIterator& other) const {
+        return !(*this == other);
+    }
+
+#pragma endregion
+
+#pragma region Lazy Split
+
+    LazySplit::LazySplit(const std::u8string_view& strl, const std::u8string_view& delimiter) : m_strl(strl), m_delimiter(delimiter) {}
+
+    LazySplitIterator LazySplit::begin() const {
+        return LazySplitIterator(m_strl, m_delimiter);
+    }
+
+    LazySplitIterator LazySplit::end() const {
+        // Pass std::nullopt to indicate end.
+        return LazySplitIterator(std::nullopt, m_delimiter);
+    }
+
+#pragma endregion
+
+    LazySplit lazy_split(const std::u8string_view& strl, const std::u8string_view& delimiter) {
+        return LazySplit(strl, delimiter);
+    }
+
+    std::vector<std::u8string_view> split(const std::u8string_view& strl, const std::u8string_view& delimiter) {
+        // use lazy split iterator to do the splitting
         std::vector<std::u8string_view> elems;
-
+        for (const auto& strl_view : lazy_split(strl, delimiter)) {
-        // if string need to be splitted is empty, return original string (empty string).
+            elems.emplace_back(strl_view);
-        // if delimiter is empty, return original string.
-        std::u8string delimiter(_delimiter);
-        if (strl.empty() || delimiter.empty()) {
-            elems.emplace_back(strl);
-            return elems;
-        }
-
-        // start spliting
-        std::size_t previous = 0, current;
-        while ((current = strl.find(delimiter.c_str(), previous)) != std::u8string::npos) {
-            elems.emplace_back(strl.substr(previous, current - previous));
-            previous = current + delimiter.size();
-        }
-        // try insert last part but prevent possible out of range exception
-        if (previous <= strl.size()) {
-            elems.emplace_back(strl.substr(previous));
         }
         return elems;
     }
 
-    std::vector<std::u8string> split_owned(const std::u8string_view& strl, const std::u8string_view& _delimiter) {
+    std::vector<std::u8string> split_owned(const std::u8string_view& strl, const std::u8string_view& delimiter) {
-        // call split view
+        // use lazy split iterator to do the splitting
-        auto view_result = split(strl, _delimiter);
-
-        // copy string view result to string
         std::vector<std::u8string> elems;
-        elems.reserve(view_result.size());
+        for (const auto& strl_view : lazy_split(strl, delimiter)) {
-        for (const auto& strl_view : view_result) {
             elems.emplace_back(std::u8string(strl_view));
         }
-        // return copied result
         return elems;
     }
 

src/yycc/string/op.hpp

@@ -5,6 +5,7 @@
 #include <cstdarg>
 #include <functional>
 #include <vector>
+#include <optional>
 
 namespace yycc::string::op {
 
@@ -125,33 +126,93 @@ namespace yycc::string::op {
     // TODO:
     // Add strip, lstrip and rstrip functions.
 
+#pragma region Split
+
+    /**
+     * @brief Iterator class for lazy splitting of strings.
+     */
+    class LazySplitIterator {
+    public:
+        using iterator_category = std::forward_iterator_tag;
+        using value_type = std::u8string_view;
+        using difference_type = std::ptrdiff_t;
+        using pointer = const std::u8string_view*;
+        using reference = const std::u8string_view&;
+
+    private:
+        /**
+         * @brief Current splitted item.
+         * @details Currently already splitted item for user fetching.
+         * If this value is std::nullopt, it means that we are reach the split process endpoint.
+         */
+        std::optional<std::u8string_view> m_current_str;
+        /**
+         * @brief The string passed to the next of iterator.
+         * @details It actually the remains after split excluding delimiter.
+         */
+        std::optional<std::u8string_view> m_next_str;
+        std::u8string_view m_delimiter; ///< Delimiter
+
+    public:
+        LazySplitIterator(std::optional<std::u8string_view> strl, const std::u8string_view& delimiter);
+
+        reference operator*() const;
+        pointer operator->() const;
+        LazySplitIterator& operator++();
+        LazySplitIterator operator++(int);
+        bool operator==(const LazySplitIterator& other) const;
+        bool operator!=(const LazySplitIterator& other) const;
+    };
+
+    /**
+     * @brief Class for lazy splitting of strings.
+     */
+    class LazySplit {
+    private:
+        std::u8string_view m_strl;      ///< Original string
+        std::u8string_view m_delimiter; ///< Delimiter
+
+    public:
+        LazySplit(const std::u8string_view& strl, const std::u8string_view& delimiter);
+        LazySplitIterator begin() const;
+        LazySplitIterator end() const;
+    };
+
+    /**
+     * @brief Lazily split given string with specified delimiter.
+     * @param[in] strl The string need to be splitting.
+     * @param[in] delimiter The delimiter for splitting.
+     * @return
+     * LazySplit object that can be used in range-based for loops.
+     * \par
+     * Every items in result is a splitted entries.
+     * If given string or delimiter are empty,
+     * the result container will only contain one entry which is equal to given string.
+     */
+    LazySplit lazy_split(const std::u8string_view& strl, const std::u8string_view& delimiter);
     /**
      * @brief Split given string with specified delimiter as string view.
+     * @details
+     * If your split involve large items, please consider using lazy_split(),
+     * because it split entries one by one rather than one time output.
      * @param[in] strl The string need to be splitting.
-     * @param[in] _delimiter The delimiter for splitting.
+     * @param[in] delimiter The delimiter for splitting.
-     * @return
+     * @return Split result in string view format.
-     * The split result with string view format.
+     * @see lazy_split() for more about aplit rules.
-     * This will not produce any copy of original string.
-     * \par
-     * If given string or delimiter are empty,
-     * the result container will only contain 1 entry which is equal to given string.
-     * @see Split(const std::u8string_view&, const char8_t*)
     */
-    std::vector<std::u8string_view> split(const std::u8string_view& strl, const std::u8string_view& _delimiter);
+    std::vector<std::u8string_view> split(const std::u8string_view& strl, const std::u8string_view& delimiter);
     /**
 	 * @brief Split given string with specified delimiter.
+     * @details
+     * If there is no requirement about storing result, 
+     * please consider using split() becuase it use less memory.
 	 * @param[in] strl The string need to be splitting.
-	 * @param[in] _delimiter The delimiter for splitting.
+	 * @param[in] delimiter The delimiter for splitting.
-	 * @return 
+	 * @return Split result in string format.
-	 * The split result.
+     * @see lazy_split() for more about aplit rules.
-	 * \par
-	 * If given string or delimiter are empty,
-	 * the result container will only contain 1 entry which is equal to given string.
 	*/
-    std::vector<std::u8string> split_owned(const std::u8string_view& strl, const std::u8string_view& _delimiter);
+    std::vector<std::u8string> split_owned(const std::u8string_view& strl, const std::u8string_view& delimiter);
 
-    // TODO:
+#pragma endregion
-    // Add lazy_split(const std::u8string_view& strl, const std::u8string_view& _delimiter);
-    // Once we add it, we need redirect all split function into it.
 
 } // namespace yycc::string::op