<table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Issue</th>
<td>
<a href=https://github.com/llvm/llvm-project/issues/57208>57208</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>
Regression in call to `std::copy`
</td>
</tr>
<tr>
<th>Labels</th>
<td>
new issue
</td>
</tr>
<tr>
<th>Assignees</th>
<td>
</td>
</tr>
<tr>
<th>Reporter</th>
<td>
JohelEGP
</td>
</tr>
</table>
<pre>
See https://godbolt.org/z/PWEhj4Wds.
```C++
#include <algorithm>
#include <iterator>
template <class F>
class FunctionOutputIterator {
public:
using difference_type = void;
using iterator_category = std::output_iterator_tag;
using pointer = void;
using reference = void;
using value_type = void;
explicit FunctionOutputIterator(const F &action) : action_(action) {}
explicit FunctionOutputIterator(F &&action) : action_(std::move(action)) {}
template<class T, class = decltype(std::declval<F&>()(std::declval<T&&>()))>
void operator=(T &&value)
{
action_(static_cast<T&&>(value));
}
FunctionOutputIterator &operator*() { return *this; }
FunctionOutputIterator &operator++() { return *this; }
FunctionOutputIterator &operator++(int) { return *this; }
private:
F action_;
};
int main()
{
auto lam = [](auto&& u) {
u += 1;
};
FunctionOutputIterator f(lam);
int a[10];
std::copy(a, a+10, f);
}
```
```
<source>:32:11: error: no viable overloaded '+='
u += 1;
~ ^ ~
<source>:16:40: note: in instantiation of function template specialization 'main()::(anonymous class)::operator()<const FunctionOutputIterator<(lambda at <source>:31:16)> &>' requested here
template<class T, class = decltype(std::declval<F&>()(std::declval<T&&>()))>
^
<source>:17:10: note: in instantiation of default argument for 'operator=<const FunctionOutputIterator<(lambda at <source>:31:16)> &>' required here
void operator=(T &&value)
^~~~~~~~~~~~~~~~~~~~
/opt/compiler-explorer/clang-trunk-20220817/bin/../include/c++/v1/__type_traits/is_assignable.h:26:83: note: while substituting deduced template arguments into function template 'operator=' [with T = const FunctionOutputIterator<(lambda at <source>:31:16)> &, $1 = (no value)]
struct _LIBCPP_TEMPLATE_VIS is_assignable : _BoolConstant<__is_assignable(_Tp, _Up)> { };
^
/opt/compiler-explorer/clang-trunk-20220817/bin/../include/c++/v1/__type_traits/is_copy_assignable.h:25:14: note: in instantiation of template class 'std::is_assignable<FunctionOutputIterator<(lambda at <source>:31:16)> &, const FunctionOutputIterator<(lambda at <source>:31:16)> &>' requested here
: public is_assignable<typename add_lvalue_reference<_Tp>::type,
^
/opt/compiler-explorer/clang-trunk-20220817/bin/../include/c++/v1/__utility/pair.h:265:25: note: in instantiation of template class 'std::is_copy_assignable<FunctionOutputIterator<(lambda at <source>:31:16)>>' requested here
is_copy_assignable<second_type>::value,
^
/opt/compiler-explorer/clang-trunk-20220817/bin/../include/c++/v1/__algorithm/copy.h:92:25: note: in instantiation of template class 'std::pair<int *, FunctionOutputIterator<(lambda at <source>:31:16)>>' requested here
pair<_InIter, _OutIter> __copy(_InIter __first, _Sent __last, _OutIter __result) {
^
/opt/compiler-explorer/clang-trunk-20220817/bin/../include/c++/v1/__algorithm/copy.h:103:15: note: in instantiation of function template specialization 'std::__copy<int *, int *, FunctionOutputIterator<(lambda at <source>:31:16)>, 0>' requested here
return std::__copy(__first, __last, __result).second;
^
<source>:36:10: note: in instantiation of function template specialization 'std::copy<int *, FunctionOutputIterator<(lambda at <source>:31:16)>>' requested here
std::copy(a, a+10, f);
^
<source>:32:11: error: no viable overloaded '+='
u += 1;
~ ^ ~
<source>:16:40: note: in instantiation of function template specialization 'main()::(anonymous class)::operator()<FunctionOutputIterator<(lambda at <source>:31:16)>>' requested here
template<class T, class = decltype(std::declval<F&>()(std::declval<T&&>()))>
^
<source>:17:10: note: in instantiation of default argument for 'operator=<FunctionOutputIterator<(lambda at <source>:31:16)>>' required here
void operator=(T &&value)
^~~~~~~~~~~~~~~~~~~~
/opt/compiler-explorer/clang-trunk-20220817/bin/../include/c++/v1/__type_traits/is_assignable.h:26:83: note: while substituting deduced template arguments into function template 'operator=' [with T = FunctionOutputIterator<(lambda at <source>:31:16)>, $1 = (no value)]
struct _LIBCPP_TEMPLATE_VIS is_assignable : _BoolConstant<__is_assignable(_Tp, _Up)> { };
^
/opt/compiler-explorer/clang-trunk-20220817/bin/../include/c++/v1/__type_traits/is_move_assignable.h:26:14: note: in instantiation of template class 'std::is_assignable<FunctionOutputIterator<(lambda at <source>:31:16)> &, FunctionOutputIterator<(lambda at <source>:31:16)> &&>' requested here
: public is_assignable<typename add_lvalue_reference<_Tp>::type,
^
/opt/compiler-explorer/clang-trunk-20220817/bin/../include/c++/v1/__utility/pair.h:278:25: note: in instantiation of template class 'std::is_move_assignable<FunctionOutputIterator<(lambda at <source>:31:16)>>' requested here
is_move_assignable<second_type>::value,
^
/opt/compiler-explorer/clang-trunk-20220817/bin/../include/c++/v1/__algorithm/copy.h:92:25: note: in instantiation of template class 'std::pair<int *, FunctionOutputIterator<(lambda at <source>:31:16)>>' requested here
pair<_InIter, _OutIter> __copy(_InIter __first, _Sent __last, _OutIter __result) {
^
/opt/compiler-explorer/clang-trunk-20220817/bin/../include/c++/v1/__algorithm/copy.h:103:15: note: in instantiation of function template specialization 'std::__copy<int *, int *, FunctionOutputIterator<(lambda at <source>:31:16)>, 0>' requested here
return std::__copy(__first, __last, __result).second;
^
<source>:36:10: note: in instantiation of function template specialization 'std::copy<int *, FunctionOutputIterator<(lambda at <source>:31:16)>>' requested here
std::copy(a, a+10, f);
^
2 errors generated.
Compiler returned: 1
```
</pre>
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