feat: add and use utf8subview

include/dpp/utility.h

@@ -746,6 +746,18 @@ std::string DPP_EXPORT debug_dump(uint8_t* data, size_t length);
  */
 size_t DPP_EXPORT utf8len(std::string_view str);
 
+/**
+ * @brief Return subview of a UTF-8 encoded string in codepoints.
+ * @note You must ensure that the resulting view is not used after the lifetime of the viewed string has ended.
+ * @note Result is unspecified for strings that are not valid UTF-8.
+ *
+ * @param str string to return substring from
+ * @param start start codepoint offset
+ * @param length length in codepoints
+ * @return std::string_view The requested subview
+ */
+std::string_view DPP_EXPORT utf8subview(std::string_view str, size_t start, size_t length);
+
 /**
  * @brief Return substring of a UTF-8 encoded string in codepoints.
  * @note Result is unspecified for strings that are not valid UTF-8.

src/dpp/commandhandler.cpp

@@ -168,7 +168,7 @@ bool commandhandler::string_has_prefix(std::string &str)
 {
 	for (auto& p : prefixes) {
 		size_t prefix_length = utility::utf8len(p);
-		if (utility::utf8substr(str, 0, prefix_length) == p) {
+		if (utility::utf8subview(str, 0, prefix_length) == p) {
 			str.erase(str.begin(), str.begin() + prefix_length);
 			return true;
 		}

src/dpp/utility.cpp

@@ -505,7 +505,7 @@ size_t utf8len(std::string_view str) {
 	return code_points;
 }
 
-std::string utf8substr(std::string_view str, size_t start, size_t length) {
+std::string_view utf8subview(std::string_view str, size_t start, size_t length) {
 	/* Shouldn't rely on signedness of char, better cast to unsigned char */
 	const auto* const s = reinterpret_cast<const unsigned char*>(str.data());
 
@@ -537,7 +537,11 @@ std::string utf8substr(std::string_view str, size_t start, size_t length) {
 		code_points += 1;
 	}
 
-	return std::string(str.substr(subview_start, subview_len));
+	return str.substr(subview_start, subview_len);
+}
+
+std::string utf8substr(std::string_view str, size_t start, size_t length) {
+	return std::string(utf8subview(str, start, length));
 }
 
 std::string read_file(const std::string& filename)