non-allocating element() variant on ListParser

include/cubescript/cubescript.hh

@@ -771,6 +771,15 @@ namespace util {
         ostd::Size parse(ostd::Size n);
         ostd::Size count();
 
+        template<typename R>
+        ostd::Size element(R &&writer) const {
+            if (!quote.empty() && (*quote == '"')) {
+                return unescape_string(ostd::forward<R>(writer), item);
+            } else {
+                return writer.put_n(item.data(), item.size());
+            }
+        }
+
         CsString element() const;
 
 private:

src/cs_util.cc

@@ -392,18 +392,9 @@ endblock:
     }
 
     CsString ListParser::element() const {
-        CsString s;
+        auto app = ostd::appender<CsString>();
-        s.reserve(item.size());
+        element(app);
-        if (!quote.empty() && (*quote == '"')) {
+        return ostd::move(app.get());
-            auto writer = s.iter_cap();
-            util::unescape_string(writer, item);
-            writer.put('\0');
-        } else {
-            memcpy(s.data(), item.data(), item.size());
-            s[item.size()] = '\0';
-        }
-        s.advance(item.size());
-        return s;
     }
 } /* namespace util */