clang-tidy - cppcoreguidelines-rvalue-reference-param-not-moved — Extra Clang Tools 22.1.8 documentation

# Extra Clang Tools 22.1.8 documentation

## clang-tidy - cppcoreguidelines-rvalue-reference-param-not-moved

# cppcoreguidelines-rvalue-reference-param-not-moved

Warns when an rvalue reference function parameter is never moved within the function body.

Rvalue reference parameters indicate a parameter that should be moved with `std::move` from within the function body. Any such parameter that is never moved is confusing and potentially indicative of a buggy program.

Example:

    void logic(std::string&& Input) {
      std::string Copy(Input); // Oops - forgot to std::move
    }

Note that parameters that are unused and marked as such will not be diagnosed.

Example:

    void conditional_use([[maybe_unused]] std::string&& Input) {
      // No diagnostic here since Input is unused and marked as such
    }

## Options

AllowPartialMove

  > If set to true, the check accepts `std::move` calls containing any subexpression containing the parameter. CppCoreGuideline F.18 officially mandates that the parameter itself must be moved. Default is false.

      // 'p' is flagged by this check if and only if AllowPartialMove is false
      void move_members_of(pair<Obj, Obj>&& p) {
        pair<Obj, Obj> other;
        other.first = std::move(p.first);
        other.second = std::move(p.second);
      }

      // 'p' is never flagged by this check
      void move_whole_pair(pair<Obj, Obj>&& p) {
        pair<Obj, Obj> other = std::move(p);
      }

IgnoreUnnamedParams

  If set to true, the check ignores unnamed rvalue reference parameters. Default is false.

IgnoreNonDeducedTemplateTypes

  > If set to true, the check ignores non-deduced template type rvalue reference parameters. Default is false.

      template <class T>
      struct SomeClass {
        // Below, 'T' is not deduced and 'T&&' is an rvalue reference type.
        // This will be flagged if and only if IgnoreNonDeducedTemplateTypes is
        // false. One suggested fix would be to specialize the class for 'T' and
        // 'T&' separately (e.g., see std::future), or allow only one of 'T' or
        // 'T&' instantiations of SomeClass (e.g., see std::optional).
        SomeClass(T&& t) { }
      };

      // Never flagged, since 'T' is a forwarding reference in a deduced context
      template <class T>
      void forwarding_ref(T&& t) {
        T other = std::forward<T>(t);
      }

MoveFunction

  Specify the function used for moving. Default is ::std::move.

This check implements F.18 from the C++ Core Guidelines.