US303 24.07.5.2 Constrain return type of transformation function for transform_view LWG 3325 #299
Description
The transform_view does not constrain the return type of the transformation function. It is invalid to pass a void-returning transformation function to the transform_view, which would cause its iterators’ operator* member to return void.
Proposed change:
Change the constraints on transform_view to the following:
template<input_range V, copy_constructible F> requires view<V> && is_object_v<F> && regular_invocable<F&, range_reference_t<V>> && can-reference<:invoke_result_t<F&, range_reference_t<V>>> class transform_view