std::forward forwards lvalues either as lvalues or as rvalues based on its template argument.
std::forward should always take as a non-template argument a forwarding reference which is defined by the standard as:
rvalue reference to a cv-unqualified template parameter that does not represent a template parameter of a class template.
If you don’t pass forwarding reference as an argument to std::forward S5417 will be triggered.
If you don’t pass the template parameter referred to by the forwarded reference or the decltype of the forwarded expression this rule
will be triggered.
Noncompliant code example
template <class T>
void g(T&& t);
template <class T>
void f(T&& t) {
g(std::forward<T&&>(t)); // Noncompliant
g(std::forward<T&>(t)); // Noncompliant
}
Compliant solution
template <class T>
void g(T&& t);
template <class T>
void f(T&& t) {
g(std::forward<T>(t)); // Compliant
}
struct StrWrapper {
std::string s = "rand";
std::string getStr() && {
return s;
}
std::string& getStr() & {
return s;
}
};
template <class T>
void fstr(T&& str);
template <class T>
void wrapper(T&& strWrapper ) {
fstr(forward<decltype(forward<T>(strWrapper).getStr())>(forward<T>(strWrapper).getStr())); // Compliant
}
