Or are you looking for a way to specify an explicit template constructor argument list? Possibly with T& reference type? This would be possible for non-constructor template functions.   Currently the standard says as note: https://timsong-cpp.github.io/cppwp/temp.arg.explicit#8 [Note 4:  Because the explicit template argument list follows the function template name, and because constructor templates ([class.ctor]) are named without using a function name ([class.qual]), there is no way to provide an explicit template argument list for these function templates. — end note]     -----Ursprüngliche Nachricht----- Von:David wang via Std-Proposals <std-proposals_at_[hidden]> Gesendet:Di 07.05.2024 09:46 Betreff:[std-proposals] Pass derived object by reference to single parameter delegated templated constructors An:C++ <std-proposals_at_[hidden]>; CC:David wang <wangjufan_at_[hidden]>; On Mon, 6 May 2024 10:18:35 -0400  Jason McKesson via Std-Proposals <std-proposals_at_[hidden] <mailto:std-proposals_at_[hidden]> > wrote: >This is way too special-case to implement. It's ultimately on the user >to prevent this from happening. `base`'s constructor uses template >argument deduction. That function takes its parameter by value. If you >use template argument deduction on such a function and pass it a type >which is a reference, it will copy the parameter. This *needs* to be a >hard-and-fast rule.  It is a special case. It is a conflict between rule and best practices. But It is not the user's fault. Rules and practices may change or be refined by us.   -- Std-Proposals mailing list Std-Proposals_at_[hidden] https://lists.isocpp.org/mailman/listinfo.cgi/std-proposals