minor issues in <xutility>

[achabense]

Below is the current code in <xutility>. At line 879, it seems incrementable_traits lacks _EXPORT_STD.

And as to projected at line 867, it seems the definition of operator*() is not needed. (cppreference:"projected is used only to constrain algorithms that accept callable objects and projections, and hence its operator*() is not defined.")

[frederick-vs-ja]

1. <xutility> only provides a partial specialization of incrementable_traits, while the primary template is defined in <__msvc_iter_core.hpp> and exported. Whenever the primary template is exported, so are its specializations, and thus it's totally fine to omit _EXPORT_STD here
   

   STL/stl/inc/__msvc_iter_core.hpp

   Lines 61 to 62 in 5404ba9

   	_EXPORT_STD template <class>
   	struct incrementable_traits {};

2. The function body is a permanent workaround for a bug of MSVC (see Standard Library Header Units and Modules - tracking issue #1694), so perhaps it's not time to remove it at this moment. Although I'm not sure whether _STL_UNREACHABLE would be better.

[StephanTLavavej]

@achabense In the future, when reporting issues, it's better to use GitHub permalinks instead of screenshots. This makes navigating to the source file and context easy, allows copy-pasting, and is more accessible. For example, if I mention:

https://github.com/microsoft/STL/blob/5404ba9c25f26f25a0ac50e6c4defce7833a8da6/stl/inc/xutility#L866-L882

then it's displayed as:

STL/stl/inc/xutility

Lines 866 to 882 in 5404ba9

	_EXPORT_STD template <indirectly_readable _It, indirectly_regular_unary_invocable<_It> _Proj>
	struct projected {
	using value_type = remove_cvref_t<indirect_result_t<_Proj&, _It>>;
	indirect_result_t<_Proj&, _It> operator*() const {
	_CSTD abort();
	}
	};
	template <class _It, class _Proj>
	struct _Indirect_value_impl<projected<_It, _Proj>> {
	using type = invoke_result_t<_Proj&, _Indirect_value_t<_It>>;
	};
	template <weakly_incrementable _It, class _Proj>
	struct incrementable_traits<projected<_It, _Proj>> {
	using difference_type = iter_difference_t<_It>;
	};

See Creating a permanent link to a code snippet.