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// { dg-do compile { target c++17 } }
template <class T> struct A {
using value_type = T;
A(value_type); // #1
A(const A&); // #2
A(T, T, int); // #3
template<class U> A(int, T, U); // #4
}; // A(A); #5, the copy deduction candidate
A x (1, 2, 3); // uses #3, generated from a non-template constructor
template <class T> A(T) -> A<T>; // #6, less specialized than #5
A a (42); // uses #6 to deduce A<int> and #1 to initialize
A b = a; // uses #5 to deduce A<int> and #2 to initialize
template <class T> A(A<T>) -> A<A<T>>; // #7, as specialized as #5
A b2 = a; // uses #7 to deduce A<A<int>> and #1 to initialize
template <class,class> struct same;
template <class T> struct same<T,T> {};
same<decltype(a),A<int>> s1;
same<decltype(b),A<int>> s2;
same<decltype(b2),A<A<int>>> s3;
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