transform_iterator merely input_iterator when not const callable

OleErikPeistorpet · May 26, 2024 · 7736266 · 7736266
1 parent def2962
commit 7736266
Show file tree

Hide file tree

Showing 2 changed files with 8 additions and 6 deletions.
diff --git a/unit_test/view_gtest.cpp b/unit_test/view_gtest.cpp
@@ -212,7 +212,7 @@ TEST(viewTest, viewTransformMutableLambda)
 	auto v = view::transform(dummy, iota);
 	using I = decltype(v.begin());
 
-	static_assert(std::is_same_v<I::iterator_category, std::bidirectional_iterator_tag>);
+	static_assert(std::is_same_v<I::iterator_category, std::input_iterator_tag>);
 #if OEL_STD_RANGES
 	static_assert(std::input_or_output_iterator<I>);
 	static_assert(std::ranges::range<decltype(v)>);

diff --git a/view/transform_iterator.h b/view/transform_iterator.h
@@ -26,11 +26,13 @@ class transform_iterator
 {
 	_detail::TightPair< Iterator, typename _detail::AssignableWrap<UnaryFunc>::Type > _m;
 
-	static constexpr bool _isBidirectional = iter_is_bidirectional<Iterator>;
+	inline static constexpr auto _isBidirectional = iter_is_bidirectional<Iterator>;
+	inline static constexpr auto _isConstCallable = std::is_invocable_v< UnaryFunc const, decltype(*_m.first) >;
 
 public:
-	using iterator_category = std::conditional_t<
-			std::is_copy_constructible_v<UnaryFunc>,
+	using iterator_category =
+		std::conditional_t<
+			std::is_copy_constructible_v<UnaryFunc> and _isConstCallable,
 			std::conditional_t<
 				_isBidirectional,
 				std::bidirectional_iterator_tag,
@@ -50,7 +52,7 @@ class transform_iterator
 	constexpr const Iterator & base() const & noexcept  OEL_ALWAYS_INLINE { return _m.first; }
 
 	constexpr reference operator*() const
-		OEL_REQUIRES(std::invocable< UnaryFunc const, decltype(*_m.first) >)
+		OEL_REQUIRES(_isConstCallable)
 		{
 			const UnaryFunc & f = _m.second();
 			return f(*_m.first);
@@ -100,7 +102,7 @@ class transform_iterator
 		(const transform_iterator & left, sentinel_wrapper<S> right)   { return left._m.first - right._s; }
 
 	constexpr bool operator==(const transform_iterator & right) const   { return _m.first == right._m.first; }
-
+	// These are not hidden friends because MSC 2017 gives error C3615
 	constexpr bool operator!=(const transform_iterator & right) const   { return _m.first != right._m.first; }
 
 	template< typename S >