1 // { dg-do compile { target c++17 } }
2 
3 template <class T> struct A {
4   using value_type = T;
5   A(value_type); // #1
6   A(const A&); // #2
7   A(T, T, int); // #3
8   template<class U> A(int, T, U); // #4
9 }; // A(A); #5, the copy deduction candidate
10 
11 A x (1, 2, 3); // uses #3, generated from a non-template constructor
12 
13 template <class T> A(T) -> A<T>;  // #6, less specialized than #5
14 
15 A a (42); // uses #6 to deduce A<int> and #1 to initialize
16 A b = a;  // uses #5 to deduce A<int> and #2 to initialize
17 
18 template <class T> A(A<T>) -> A<A<T>>;  // #7, as specialized as #5
19 
20 A b2 = a;  // uses #7 to deduce A<A<int>> and #1 to initialize
21 
22 template <class,class> struct same;
23 template <class T> struct same<T,T> {};
24 
25 same<decltype(a),A<int>> s1;
26 same<decltype(b),A<int>> s2;
27 same<decltype(b2),A<A<int>>> s3;
28