AutosarC++18_10-A18.9.2

Forwarding values to other functions shall be done via: (1) std::move if the value is an rvalue reference, (2) std::forward if the value is forwarding reference

Required inputs: IR

When forwarding values to other functions, use the correct utility: std::move for rvalue references and std::forward for forwarding references (template parameters that deduce both lvalue and rvalue). Using the wrong utility defeats move semantics or creates unnecessary copies, effectively reducing performance.

Bad code (std::move with forwarding reference):

void Process(std::string&& str);
void Process(const std::string& str);

template<typename T>
void Forward(T&& value) {             // Forwarding reference: T&& accepts both lvalue and rvalue
    Process(std::move(value));        // ERROR: std::move unconditionally casts to rvalue,
    // ignoring what T deduced to. When called with an lvalue, std::move silently steals
    // from the caller's object.
}

int main() {
    std::string s = "hello";
    Forward(s);                    // lvalue call: caller expects s to remain valid afterward,
                                   // but s is moved-from and thus left in an unspecified state
    Forward(std::string("hello")); // rvalue call: happens to work, but std::forward is still correct
}

Good code (std::forward for forwarding reference):

template<typename T>
void Forward(T&& value) {
    Process(std::forward<T>(value));    // OK: preserves lvalue/rvalue
}

Possible Messages

Key	Text	Severity	Disabled
forwarding_forwarding_reference	Use std::forward if the value is a forwarding reference.	None	False
forwarding_rvalue_reference	Use std::move if the value is a rvalue reference.	None	False

Options

• This rule shares the following common options: exclude_in_macros, exclude_messages_in_system_headers, excludes, extend_exclude_to_macro_invocations, includes, justification_checker, languages, post_processing, provider, report_at, severity

• The following places define options that affect this rule: Stylechecks, Analysis-GlobalOptions

allow_forward_decltype

allow_forward_decltype : bool = False

If set to true, consider decltype(..Template-Parameter..) as a forwarding reference and do not produce violations on std::forward(...).