c++ - Variadic templates argument fowarding -

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say have function foo() takes advantage of c++ variadic templates feature. now, what's difference between these implementations:

template <typename... args> void foo(args... args) { whatever(args...); }  template<typename... args> void foo(args&... args) { whatever(args...); }  template<typename... args> void foo(args... args) { whatever(&args...); }  template<typename... args> void foo(args&&... args) { whatever(std::forward<args>(args)...); } 

template <typename... args> void foo(args... args) {     whatever(args...); }

foo gets copies of args , passes them whatever l-values.

template<typename... args>  void foo(args&... args) {      whatever(args...); }

foo gets l-value references args , passes them whatever l-values.

template<typename... args> void foo(args... args) {     whatever(&args...); }

foo gets copies of args , passes them whatever pointers l-values. careful of object lifetimes here.

template<typename... args> void foo(args&&... args) {     whatever(std::forward<args>(args)...); }

foo gets forwarding references args. whether l-values or r-values depends on happens @ call site. perfect-forwarded whatever, preserving reference type. scott meyers called these "universal" references, forwarding reference preferred terminology now.


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