Function StringContains

external/utf8-cpp-utils/test/doctest.h:852–852

        public:
            StringContains(const String& str) : content(str), isContains(false) { }
            StringContains(Contains cntn) : content(static_cast<Contains&&>(cntn)), isContains(true) { }

            bool check(const String& str) { return isContains ? (content == str) : (content.string == str); }