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);
}

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