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template<class T>
struct wrapper { T t; };
 
// Checks if the type is instantiated from the wrapper
template <typename...>
struct sfinae_without_wrapper {};
 
template <typename H, typename... T>
struct sfinae_without_wrapper<H, T...> { typedef typename sfinae_without_wrapper<T...>::type type; };
 
template <typename H, typename... T>
struct sfinae_without_wrapper<wrapper<H>, T...> { typedef H type; };
 
// Returns the underlying object
template <typename T> T const& base(T const& t)          { return   t; }
template <typename T> T const& base(wrapper<T> const& w) { return w.t; }
 
// Operator
template<class W, class X>
auto operator+(const W& i, const X& j) ->
    decltype(typename sfinae_without_wrapper<W, X>::type{}, base(i) + base(j))
{
    return base(i) + base(j);
}
 
// Test case
struct test { int i; };
 
int main() {
    test{1} + test{2};
    return 0;
}

prog.cpp: In instantiation of ‘struct sfinae_without_wrapper<test>’:
prog.cpp:9:94:   required from ‘struct sfinae_without_wrapper<test, test>’
prog.cpp:21:59:   required by substitution of ‘template<class W, class X> decltype ((typename sfinae_without_wrapper<W, X>::type{}, (base(i) + base(j)))) operator+(const W&, const X&) [with W = test; X = test]’
prog.cpp:30:21:   required from here
prog.cpp:9:94: error: no type named ‘type’ in ‘struct sfinae_without_wrapper<>’
 struct sfinae_without_wrapper<H, T...> { typedef typename sfinae_without_wrapper<T...>::type type; };
                                                                                              ^
prog.cpp:21:77: error: template instantiation depth exceeds maximum of 900 (use -ftemplate-depth= to increase the maximum) substituting ‘template<class T> const T& base(const T&) [with T = test]’
     decltype(typename sfinae_without_wrapper<W, X>::type{}, base(i) + base(j))
                                                                             ^
prog.cpp:21:69:   recursively required by substitution of ‘template<class W, class X> decltype ((typename sfinae_without_wrapper<W, X>::type{}, (base(i) + base(j)))) operator+(const W&, const X&) [with W = test; X = test]’
prog.cpp:21:69:   required by substitution of ‘template<class W, class X> decltype ((typename sfinae_without_wrapper<W, X>::type{}, (base(i) + base(j)))) operator+(const W&, const X&) [with W = test; X = test]’
prog.cpp:30:21:   required from here

prog.cpp: In function ‘int main()’:
prog.cpp:30:13: error: no match for ‘operator+’ (operand types are ‘test’ and ‘test’)
     test{1} + test{2};
             ^
prog.cpp:30:13: note: candidate is:
prog.cpp:20:6: note: template<class W, class X> decltype ((typename sfinae_without_wrapper<W, X>::type{}, (base(i) + base(j)))) operator+(const W&, const X&)
 auto operator+(const W& i, const X& j) ->
      ^
prog.cpp:20:6: note:   substitution of deduced template arguments resulted in errors seen above

Standard output is empty