1 // { dg-do compile { target c++17 } }
2 
3 template <class T> struct A {
4   A(T); // #1
5   A(const A&); // #2
6 };
7 
8 template <class T> A(T) -> A<T>;  // #3
9 
10 A a (42); // uses #3 to deduce A<int> and initializes with #1
11 A b = a;  // uses #2 (not #3) to deduce A<int> and initializes with #2; #2 is more specialized
12 
13 template <class T> A(A<T>) -> A<A<T>>;  // #4
14 
15 A b2 = a;  // uses #4 to deduce A<A<int>> and initializes with #1; #4 is as specialized as #2
16 
17 template <class,class> struct same;
18 template <class T> struct same<T,T> {};
19 
20 same<decltype(a),A<int>> s1;
21 same<decltype(b),A<int>> s2;
22 same<decltype(b2),A<A<int>>> s3;
23