c++ - Can a forwarding reference be aliased with an alias template? -


this continuation of previous question:

can identity alias template forwarding reference?

it seems following code works in both clang 3.7.0 (demo) , gcc 6.0.0 (demo):

template <class t> using forwarding_reference = t&&;  template <class t> void foo(forwarding_reference<t>) {}  int main() {   int i{};   foo(i);   foo(1); }

are compilers right substitute alias template forwarding reference , fancy way of writing one?

this indeed standard compliant. §14.5.7/2:

when template-id refers specialization of alias template, it equivalent associated type obtained substitution of template-arguments template-parameters in type-id of alias template.

now, consider during template argument deduction, type of parameter (in terms of template parameters) inspected - §14.8.2.1/1:

template argument deduction done comparing each function template parameter type (call p) type of corresponding argument of call (call a) described below.

according first quote, type of parameter, i.e. forwarding_reference<t>, equivalent t&&. hence p t&& , there can no difference regarding deduction.

this same conclusion made committee in defect report concerning exact scenario, #1700:

because types of function parameters same, regardless of whether written directly or via alias template, deduction must handled same way in both cases.


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