<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/105764>105764</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [libcxx] std::function doesn't with non-movable but copyable type
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            libc++
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          cw118876
      </td>
    </tr>
</table>

<pre>
    Here is a buggy test program with a std::function  :
code snipper
`#include <iostream>
#include <utility>
#include <functional>


#include <type_traits>

class Test {
   int a = 1;
   int b = 1;
public:
   Test() = default;
   Test(const Test&) = default;
 Test& operator=(const Test&) = default;

   Test(Test&&) = delete;
 Test& operator=(Test&&) =delete;
   int operator()(int first, int second) {
    return a + b + first + second;
   }
 
};


int main(int argc, const char* argv[]) {
    // std::cout << HasMember<Test>::value << "\n";
    Test t{};

 std::function<int(int, int) > f(t);
    std::cout << f(12, 123) << "\n";
    
    return 0;
}`
Compiler information: clang 18.1.0 x64
compile flags: -stdlib=libc++

compile error information:
`opt/compiler-explorer/clang-17.0.1/bin/../include/c++/v1/__memory/compressed_pair.h:60:9: error: call to deleted constructor of 'Test'
   60 |       : __value_(std::forward<_Args>(std::get<_Indices>(__args))...) {}
      | ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/opt/compiler-explorer/clang-17.0.1/bin/../include/c++/v1/__memory/compressed_pair.h:129:9: note: in instantiation of function template specialization 'std::__compressed_pair_elem<Test, 0>::__compressed_pair_elem<Test &&, 0UL>' requested here
  129 |       : _Base1(__pc, std::move(__first_args), typename __make_tuple_indices<sizeof...(_Args1)>::type()),
      | ^
/opt/compiler-explorer/clang-17.0.1/bin/../include/c++/v1/__functional/function.h:183:11: note: in instantiation of function template specialization 'std::__compressed_pair<Test, std::allocator<Test>>::__compressed_pair<Test &&, std::allocator<Test> &&>' requested here
  183 |         : __f_(piecewise_construct, _VSTD::forward_as_tuple(_VSTD::move(__f)),
 | ^
/opt/compiler-explorer/clang-17.0.1/bin/../include/c++/v1/__functional/function.h:308:11: note: in instantiation of member function 'std::__function::__alloc_func<Test, std::allocator<Test>, int (int, int)>::__alloc_func' requested here
  308 |         : __f_(_VSTD::move(__f), _VSTD::move(__a)) {}
      | ^
/opt/compiler-explorer/clang-17.0.1/bin/../include/c++/v1/__functional/function.h:424:44: note: in instantiation of member function 'std::__function::__func<Test, std::allocator<Test>, int (int, int)>::__func' requested here
  424 | ::new ((void*)&__buf_) _Fun(_VSTD::move(__f), _Alloc(__af));
      | ^
/opt/compiler-explorer/clang-17.0.1/bin/../include/c++/v1/__functional/function.h:439:11: note: in instantiation of function template specialization 'std::__function::__value_func<int (int, int)>::__value_func<Test, std::allocator<Test>>' requested here
  439 |         : __value_func(_VSTD::forward<_Fp>(__f), allocator<_Fp>()) {}
      | ^
/opt/compiler-explorer/clang-17.0.1/bin/../include/c++/v1/__functional/function.h:1111:50: note: in instantiation of function template specialization 'std::__function::__value_func<int (int, int)>::__value_func<Test, void>' requested here
 1111 | function<_Rp(_ArgTypes...)>::function(_Fp __f) : __f_(_VSTD::move(__f)) {}
      | ^
<source>:29:35: note: in instantiation of function template specialization 'std::function<int (int, int)>::function<Test, void>' requested here
   29 |     std::function<int(int, int) > f(t);
      | ^
<source>:16:4: note: 'Test' has been explicitly marked deleted here
   16 |    Test(Test&&) = delete;
`
**But this test program works with GCC**.

According to cppreference [std::function:](https://en.cppreference.com/w/cpp/utility/functional/function/function) :
`template< class F >
function( F&& f ); 
`
"Initializes the target with [std::forward](http://en.cppreference.com/w/cpp/utility/forward)<F>(f). The target is of type [std::decay](http://en.cppreference.com/w/cpp/types/decay)<F>::type."

 Maybe, problem occurs, due to forcely moving the object instead of forwarding the object in follow [code.](https://github.com/llvm/llvm-project/blob/llvmorg-18.1.0/libcxx/include/__functional/function.h)
` if (__function::__not_null(__f)) {
      _FunAlloc __af(__a);
 if (sizeof(_Fun) <= sizeof(__buf_) && is_nothrow_copy_constructible<_Fp>::value &&
 is_nothrow_copy_constructible<_FunAlloc>::value) {
        __f_ = ::new ((void*)&__buf_) _Fun**(std::move(__f)**, _Alloc(__af));
      } else {
        typedef __allocator_destructor<_FunAlloc> _Dp;
 unique_ptr<__func, _Dp> __hold(__af.allocate(1), _Dp(__af, 1));
 ::new ((void*)__hold.get()) _Fun(std::move(__f), _Alloc(__a));
 __f_ = __hold.release();
      }
    }
  }`



</pre>
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