Move some stuff out of LuaStack

luprex/cpp/core/keywords.hpp

@@ -0,0 +1,92 @@
+////////////////////////////////////////////////////////////////////
+//
+// LuaKeywordParser
+//
+// This is a helper class to help parse tables full of keywords.
+// It is meant to make it easier to write LuaDefine functions that
+// accept keyword arguments.  It helps with the following tasks:
+//
+// * It makes sure the keyword table actually is a table.
+//
+// * It makes sure that all required keywords are present.
+//
+// * It makes sure that you didn't put anything that isn't a
+//   known keyword into the keyword table.
+//
+// This module adds two fields to the table:
+//
+//  [ERROR] - stores an error message, initially nil.
+//  [FOUND] - the set of keywords successfully parsed.
+//
+// If at any time, this module detects an error, it doesn't throw.
+// Instead, it stores an error report in the table key [ERROR].
+// Later, you can check for an error string using the function
+// final_check or final_check_throw.  If an error is
+// detected when there is already an error report in the table,
+// the error report is not overwritten, so therefore, the error
+// reported is always the first error detected.
+//
+// When this module finds a keyword in the table, it adds the keyword
+// to the [FOUND] set of all keywords successfully parsed.
+//
+// If the keyword table that you pass in isn't a table at all,
+// then the keyword-fetching functions will always return false.
+// Later, when you call 'check', an appropriate error will be
+// generated.
+//
+// The lua module 'keywords' contains the same functions as this
+// C++ class.  You can write code where a C++ function does some
+// of the parsing, and the lua code does the rest of the parsing.
+//
+////////////////////////////////////////////////////////////////////
+
+#ifndef KEYWORDS_HPP
+#define KEYWORDS_HPP
+
+#include "luastack.hpp"
+
+class LuaKeywordParser {
+private:
+    LuaVar found, error, key, val;
+    LuaSpecial keytab;
+    LuaCoreStack LS;
+    bool istable;
+
+    void init(const lua_State *L, int slot);
+public:
+    LuaKeywordParser(const LuaCoreStack &LS, LuaSlot slot);
+
+    // Fetch the value of the keyword.  If the keyword is found, then the
+    // keyword is added to the [FOUND] set, the value is returned in slot,
+    // and returns true.  Otherwise, sets slot to nil and returns false.
+    bool optional(LuaSlot slot, std::string_view kw);
+
+    // Fetch the value of the keyword.  If the keyword is found, then the
+    // keyword is added to the [FOUND] set, the value is returned in slot,
+    // and returns true.  Otherwise, sets slot to nil, returns false, and
+    // stores an [ERROR] report in the keyword table.
+    bool required(LuaSlot slot, std::string_view kw);
+
+    // Check if there are any errors so far, by checking for an [ERROR]
+    // report in the keyword table.  If any error has been
+    // detected, returns an error message, otherwise, returns empty
+    // string.
+    eng::string check();
+
+    // Check if there are any errors so far, by checking for an [ERROR]
+    // report in the keyword table.  Also check that all keyword
+    // arguments present in the table are in the [FOUND] set.  If there are
+    // any errors, returns an error message, otherwise returns empty string.
+    eng::string final_check();
+
+    // If check() returns an error, throws the error using luaL_error.
+    void check_throw();
+
+    // If final_check() returns an error, throws the error using luaL_error.
+    void final_check_throw();
+
+    // Fetch the state pointer.
+    lua_State *state() const { return LS.state(); }
+};
+
+#endif // KEYWORDS_HPP