Another small tweak to tokens.

luprex/cpp/core/luastack.hpp

@@ -407,20 +407,20 @@ enum LuaTableType {
 ////////////////////////////////////////////////////////////////////
 
 struct LuaToken {
-public:
+private:
-    // Convert a base36 number into a 64-bit unsigned integer.  If the
+    // Convert a base36 number into a token.  If the base36 number is
-    // base36 number is not valid, or if it exceeds 64 bits, then return
+    // not valid, or if it exceeds 64 bits, then return maxint, ie,
-    // nullopt.  Leading zeros are not allowed.  Empty string gets parsed
+    // the invalid token.
-    // as zero.
     //
-    static constexpr std::optional<uint64_t> parse_base36(const char *str) {
+    static constexpr uint64_t parse(std::string_view str) {
         uint64_t result = 0;
         uint64_t maxint = uint64_t(-1);
+
         // Leading zeros are not allowed.
-        // Note: Token(0) is emitted as the empty string, not as '0'.
+        if ((!str.empty()) && (str[0]=='0')) return maxint;
-        if ((*str == '0')) return std::nullopt;
+
-        while (*str) {
+        for (int i = 0; i < int(str.size()); i++) {
-            char c = *str++;
+            char c = str[i];
             uint64_t digit = 0;
             if ((c >= '0') && (c <= '9')) {
                 digit = uint64_t(c - '0');
@@ -429,14 +429,13 @@ public:
             } else if ((c >= 'A') && (c <= 'Z')) {
                 digit = uint64_t(c - 'A' + 10);
             } else {
-                // Invalid digits return nullopt.
+                return maxint;
-                return std::nullopt;
             }
             // Multiply existing number by 36, then add the digit.
             // We have two checks to prevent integer overflow.
-            if (result > (maxint / 36)) return std::nullopt;
+            if (result > (maxint / 36)) return maxint;
             result *= 36;
-            if (digit > (maxint - result)) return std::nullopt;
+            if (digit > (maxint - result)) return maxint;
             result += digit;
         }
         return result;
@@ -450,20 +449,22 @@ public:
     template<class T>
     LuaToken(T arg) = delete;
 
-    // Construct a token from a short string.
+    // Construct a token from a string.
     //
-    // This is meant to be used for constants in the code.
+    // If the string is not a valid token, then this initializes the
-    // It cannot be used for runtime creation of tokens.  It is
+    // token to the invalid token.
-    // limited to 10-character tokens.
-    // 
-    // Note: using 'throw' in a consteval gives largely the
-    // effect of a static_assert.
     //
-    consteval LuaToken(const char *str) : value(0) {
+    LuaToken(std::string_view s) : value(parse(s)) {}
-        auto opt = parse_base36(str);
+
-        if (!opt.has_value()) throw "not a valid token";
+    // Construct a token from a compile-time constant string.
-        if (opt.value_or(0) > 3656158440062975) throw "token may have at most 10 characters";
+    //
-        value = opt.value_or(0);
+    // It appears that the code below throws an exception if the
+    // string is invalid.  But in reality, since this function is
+    // consteval (evaluated at compile time), the error is
+    // generated during the compilation.
+    //
+    consteval LuaToken(const char *s) : value(parse(s)) {
+        if (is_invalid()) throw "Invalid token";
     }
 
     // Construct a token from an int64.
@@ -493,6 +494,10 @@ public:
     //
     void *voidvalue() const { return (void*)value; }
 
+    // Return true if it's the invalid token.
+    //
+    constexpr bool is_invalid() { return value == uint64_t(-1); }
+
     // Convert the token to a string.
     //
     // The conversion to string consists of expressing the value