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US303 24.07.5.2 Constrain return type of transformation function for transform_view LWG 3325 #299

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wg21bot opened this issue Oct 25, 2019 · 3 comments · Fixed by cplusplus/draft#3748
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US303 24.07.5.2 Constrain return type of transformation function for transform_view LWG 3325 #299

wg21bot opened this issue Oct 25, 2019 · 3 comments · Fixed by cplusplus/draft#3748
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accepted LWG Library ranges std::ranges
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CD C++20

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@wg21bot
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wg21bot commented Oct 25, 2019

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
@wg21bot wg21bot added the LWG Library label Oct 25, 2019
@jensmaurer jensmaurer added the ranges std::ranges label Oct 25, 2019
@jwakely
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jwakely commented Nov 4, 2019

Reviewed by LWG small group on Monday morning.

@Dani-Hub
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Dani-Hub commented Nov 6, 2019

The associated issue is LWG 3325

@JeffGarland
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LWG issue is Ready as of 2019-11-07

@jensmaurer jensmaurer changed the title US303 24.07.5.2 Constrain return type of transformation function for transform_view US303 24.07.5.2 Constrain return type of transformation function for transform_view LWG 3325 Nov 7, 2019
@mclow mclow added the accepted label Jan 31, 2020
@burblebee burblebee mentioned this issue Feb 21, 2020
Merged
@jensmaurer jensmaurer added this to the CD C++20 milestone Sep 5, 2020
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LWG Poll 2: P2051R0 C++ Standard Library Issues to be moved in Prague cplusplus/draft
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@mclow @Dani-Hub @jwakely @JeffGarland @jensmaurer @wg21bot