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#include <iostream>
#include <type_traits>
 
using namespace std;
 
template <typename T>
struct A {
    A(const T&) {
        cout << "A(const A&)" << endl;
    }
    A(T&&) {
        cout << "A(T&&)" << endl;
    }
};
 
template <typename T>
A(T&&) -> A<std::remove_reference_t<T>>;
 
int main() {
    auto integer{1};
    A{1};
    A{integer};
    return 0;
}
 

prog.cpp:17:40: error: expected constructor, destructor, or type conversion before ‘;’ token
 A(T&&) -> A<std::remove_reference_t<T>>;
                                        ^
prog.cpp: In function ‘int main()’:
prog.cpp:21:6: error: missing template arguments before ‘{’ token
     A{1};
      ^
prog.cpp:22:6: error: missing template arguments before ‘{’ token
     A{integer};
      ^

Standard output is empty