std::ranges::viewable_range

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros(C++20)

Language support library

Concepts library(C++20)

Diagnostics library

Memory management library

Metaprogramming library(C++11)

General utilities library

Containers library

Iterators library

Ranges library(C++20)

Algorithms library

Strings library

Text processing library

Numerics library

Date and time library

Input/output library

Filesystem library(C++17)

Concurrency support library(C++11)

Execution control library(C++26)

Technical specifications

Symbols index

External libraries

 

Ranges library

Range access begin cbegin   end cend rbegin crbegin   rend crend size ssize   data cdata reserve_hint (C++26)   empty

Range conversions std::from_range_t std::from_range (C++23)(C++23)     to (C++23)

Dangling iterator handling dangling borrowed_iterator_t borrowed_subrange_t

Range primitives
range_size_trange_difference_trange_value_t elements_of (C++23)	iterator_tconst_iterator_tsentinel_tconst_sentinel_t (C++23)(C++23)	range_reference_trange_const_reference_trange_rvalue_reference_trange_common_reference_t (C++23)

Range concepts
range borrowed_range    common_range	sized_range viewable_range    view	input_range output_range forward_range	bidirectional_range    random_access_range contiguous_range	approximately_sized_range (C++26) constant_range (C++23)

Views
view_interface	subrange

Range factories
empty_viewviews::empty	single_viewviews::single	basic_istream_viewviews::istream	iota_viewviews::iota	repeat_viewviews::repeat (C++23)(C++23)

Range adaptors
views::all_tviews::all as_rvalue_viewviews::as_rvalue (C++23)(C++23)   filter_viewviews::filter transform_viewviews::transform take_viewviews::take take_while_viewviews::take_while common_viewviews::common views::counted to_input_viewviews::to_input (C++26)(C++26)	ref_view drop_viewviews::drop drop_while_viewviews::drop_while lazy_split_viewviews::lazy_split split_viewviews::split join_viewviews::join join_with_viewviews::join_with (C++23)(C++23)   concat_viewviews::concat (C++26)(C++26) cache_latest_viewviews::cache_latest (C++26)(C++26)	owning_view reverse_viewviews::reverse as_const_viewviews::as_const (C++23)(C++23) elements_viewviews::elements keys_viewviews::keys values_viewviews::values enumerate_viewviews::enumerate (C++23)(C++23) zip_viewviews::zip (C++23)(C++23) zip_transform_viewviews::zip_transform (C++23)(C++23)	adjacent_viewviews::adjacent (C++23)(C++23) views::pairwise (C++23) adjacent_transform_viewviews::adjacent_transform (C++23)(C++23) views::pairwise_transform (C++23) chunk_viewviews::chunk (C++23)(C++23) slide_viewviews::slide (C++23)(C++23) chunk_by_viewviews::chunk_by (C++23)(C++23) stride_viewviews::stride (C++23)(C++23) cartesian_product_viewviews::cartesian_product (C++23)(C++23)

Range generators std::generator (C++23)

Range adaptor closure objects range_adaptor_closure (C++23)

Range adaptor objects

Helper items
copyable-box movable-box (until C++23)  (C++23)	simple-view non-propagating-cache

 

Defined in header <ranges>
template<class T > concept viewable_range =     ranges::range<T>&&     ((ranges::view<std::remove_cvref_t<T>>&&       std::constructible_from<std::remove_cvref_t<T>, T>)||      (!ranges::view<std::remove_cvref_t<T>>&&       (std::is_lvalue_reference_v<T>||        (std::movable<std::remove_reference_t<T>>&&!/*is-initializer-list*/<T>))));		(since C++20)

The viewable_range concept is a refinement of range that describes a range that can be converted into a view through views::all.

The constant /*is-initializer-list*/<T> is true if and only if std::remove_cvref_t<T> is a specialization of std::initializer_list.

Example

Run this code

#include <ranges>#include <string>#include <vector>   struct valid_result {};struct invalid_result {};   template<typename T> concept valid_viewable_range =std::same_as<T, valid_result>;   template<typename T> concept invalid_viewable_range =std::same_as<T, invalid_result>;   auto test_viewable_range(std::ranges::viewable_rangeauto&&)-> valid_result;auto test_viewable_range(auto&&)-> invalid_result;   int main(){auto il ={1, 2, 3};int arr []{1, 2, 3};std::vector vec{1, 2, 3}; std::ranges::ref_view r{arr}; std::ranges::owning_view o{std::string("Hello")};   static_assert(requires {{ test_viewable_range(il)}-> valid_viewable_range;{ test_viewable_range(std::move(il))}-> invalid_viewable_range;{ test_viewable_range(arr)}-> valid_viewable_range;{ test_viewable_range(std::move(arr))}-> invalid_viewable_range;{ test_viewable_range(vec)}-> valid_viewable_range;{ test_viewable_range(std::move(vec))}-> valid_viewable_range;{ test_viewable_range(r)}-> valid_viewable_range;{ test_viewable_range(std::move(r))}-> valid_viewable_range;{ test_viewable_range(o)}-> invalid_viewable_range;{ test_viewable_range(std::move(o))}-> valid_viewable_range;{ test_viewable_range(std::ranges::ref_view(o))}-> valid_viewable_range;});}

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 3481	C++20	viewable_range accepted an lvalue of a move-only view	rejects
P2415R2	C++20	viewable_range only accepted non-view rvalues that are borrowed_range	accepts more types

See also

views::all_tviews::all (C++20)

a view that includes all elements of a range (alias template)(range adaptor object)