Introduce std::string_view into wider use (#14368)

src/script/common/c_content.cpp

@@ -1664,7 +1664,7 @@ Pointabilities read_pointabilities(lua_State *L, int index)
 			std::string name = luaL_checkstring(L, -2);
 
 			// handle groups
-			if(std::string_view(name).substr(0,6)=="group:") {
+			if (str_starts_with(name, "group:")) {
 				pointabilities.node_groups[name.substr(6)] = read_pointability_type(L, -1);
 			} else {
 				pointabilities.nodes[name] = read_pointability_type(L, -1);
@@ -1685,7 +1685,7 @@ Pointabilities read_pointabilities(lua_State *L, int index)
 			std::string name = luaL_checkstring(L, -2);
 
 			// handle groups
-			if(std::string_view(name).substr(0,6)=="group:") {
+			if (str_starts_with(name, "group:")) {
 				pointabilities.object_groups[name.substr(6)] = read_pointability_type(L, -1);
 			} else {
 				pointabilities.objects[name] = read_pointability_type(L, -1);

src/script/common/helper.cpp

@@ -25,6 +25,7 @@ extern "C" {
 #include <cmath>
 #include <irr_v2d.h>
 #include <irr_v3d.h>
+#include <string_view>
 #include "c_converter.h"
 #include "c_types.h"
 
@@ -78,11 +79,16 @@ v3f LuaHelper::readParam(lua_State *L, int index)
 }
 
 template <>
-std::string LuaHelper::readParam(lua_State *L, int index)
+std::string_view LuaHelper::readParam(lua_State *L, int index)
 {
 	size_t length;
-	std::string result;
 	const char *str = luaL_checklstring(L, index, &length);
-	result.assign(str, length);
-	return result;
+	return std::string_view(str, length);
+}
+
+template <>
+std::string LuaHelper::readParam(lua_State *L, int index)
+{
+	auto sv = readParam<std::string_view>(L, index);
+	return std::string(sv); // a copy
 }

src/script/common/helper.h

@@ -19,6 +19,8 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 
 #pragma once
 
+#include <string_view>
+
 extern "C" {
 #include <lua.h>
 }
@@ -27,23 +29,22 @@ class LuaHelper
 {
 protected:
 	/**
-	 * Read a value using a template type T from Lua State L and index
-	 *
+	 * Read a value using a template type T from Lua state L at index
 	 *
 	 * @tparam T type to read from Lua
 	 * @param L Lua state
-	 * @param index Lua Index to read
+	 * @param index Lua index to read
 	 * @return read value from Lua
 	 */
 	template <typename T>
 	static T readParam(lua_State *L, int index);
 
 	/**
-	 * Read a value using a template type T from Lua State L and index
+	 * Read a value using a template type T from Lua state L at index
 	 *
 	 * @tparam T type to read from Lua
 	 * @param L Lua state
-	 * @param index Lua Index to read
+	 * @param index Lua index to read
 	 * @param default_value default value to apply if nil
 	 * @return read value from Lua or default value if nil
 	 */
@@ -53,3 +54,18 @@ protected:
 		return lua_isnoneornil(L, index) ? default_value : readParam<T>(L, index);
 	}
 };
+
+// (only declared for documentation purposes:)
+
+/**
+ * Read a string from Lua state L at index without copying it.
+ *
+ * Note that the returned string view is only valid as long as the value is on
+ * the stack and has not been modified. Be careful.
+ *
+ * @param L Lua state
+ * @param index Lua index to read
+ * @return string view
+ */
+template <>
+std::string_view LuaHelper::readParam(lua_State *L, int index);