Make ComaptStringArray with more function

Author: Coldwings

common/conststr.h

@@ -304,8 +304,13 @@ struct EnumStr : public Split {
 template <typename Accum, typename Whole>
 struct CompactStringArray {
     constexpr static decltype(auto) whole() { return Whole(); }
+    constexpr static size_t size() { return Accum::size(); }
 
     constexpr static std::string_view at(size_t i) {
+        if (i < 0 || i >= size()) return {};
+        return CompactStringArray<Accum, Whole>()[i];
+    }
+    constexpr std::string_view operator[](size_t i) {
         return {&Whole::chars[Accum::arr[i] + i],
                 (size_t)Accum::arr[i + 1] - (size_t)Accum::arr[i]};
     }