Implements: std::ranges::any_view proposed in any_view (P3411R2).
Status: Under development and not yet ready for production use.
Featured: C++Now 2025
any_view equips library APIs with the ability to declare function parameters and return types as views, while
de-coupling the interface from an implementation that can fully leverage the power of C++20 ranges. By using
type-erased views, the library can be compiled separately.
As a return type, any_view grants a library author the freedom to change how the function is implemented to return
the view without modifying its interface. As a parameter type, it allows users to call the library function with any
range as an argument that can be consumed directly, rather than copying it into some bespoke, library-specific type.
#include <beman/any_view/any_view.hpp>
#include <ranges>
#include <vector>
namespace bav = beman::any_view;
using opt = bav::any_view_options;
template <class T>
using proxy_any_view = bav::any_view<T, opt::input, T>;
constexpr auto sum(proxy_any_view<proxy_any_view<int>> views) {
auto result = 0;
for (auto view : views) {
for (const auto value : view) {
result += value;
}
}
return result;
}
static_assert(10 == sum(std::vector{std::vector{1, 2}, std::vector{3, 4}}));
constexpr auto iota(int n) { return std::views::iota(1) | std::views::take(n); };
static_assert(35 == sum(iota(5) | std::views::transform(iota)));
static_assert(22 == sum(std::vector{iota(1), iota(3), iota(5)}));Full code can be found in tests/beman/any_view/constexpr.test.cpp.
std::ranges::any_view is a class template that provides a type-erased interface for std::ranges::view.
It may additionally model other concepts like std::ranges::contiguous_range, std::ranges::sized_range,
std::ranges::borrowed_range, and std::copyable depending on the instantiation.
Use beman.any_view directly from CMake
For CMake based projects, you can include it as a dependency using the FetchContent module:
include(FetchContent)
FetchContent_Declare(
beman.any_view
GIT_REPOSITORY https://github.com/bemanproject/any_view.git
GIT_TAG main
EXCLUDE_FROM_ALL
)
FetchContent_MakeAvailable(beman.any_view)You will also need to add beman::any_view to the link libraries of any targets that include beman/any_view/*.hpp in
their source or header files:
target_link_libraries(yourlib PUBLIC beman::any_view)Synopsis
namespace beman::any_view {
// [range.any]
enum class any_view_options {
input = 0b00000001,
forward = 0b00000011,
bidirectional = 0b00000111,
random_access = 0b00001111,
contiguous = 0b00011111,
sized = 0b00100000,
borrowed = 0b01000000,
copyable = 0b10000000,
};
constexpr any_view_options operator|(any_view_options, any_view_options) noexcept;
constexpr any_view_options operator&(any_view_options, any_view_options) noexcept;
template <class T>
struct /*rvalue-ref*/ {
using type = T;
};
template <class T>
struct /*rvalue-ref*/<T&> {
using type = T&&;
};
template <class T>
using /*rvalue-ref-t*/ = /*rvalue-ref*/<T>::type;
template <class RangeT, class AnyViewT>
concept ext_any_compatible_viewable_range = /* ... */;
template <class ElementT,
any_view_options OptsV = any_view_options::input,
class RefT = ElementT&,
class RValueRefT = /*as-rvalue-t*/<RefT>,
class DiffT = std::ptrdiff_t>
class any_view : public std::ranges::view_interface<any_view<ElementT, OptsV, RefT, RValueRefT, DiffT>> {
class iterator; // exposition-only
class sentinel; // exposition-only
public:
// [range.any.ctor]
template <class RangeT>
constexpr any_view(RangeT&& range);
constexpr any_view(const any_view&);
constexpr any_view(any_view&&) noexcept;
constexpr any_view& operator=(const any_view&);
constexpr any_view& operator=(any_view&&) noexcept;
constexpr ~any_view();
// [range.any.access]
constexpr iterator begin();
constexpr sentinel end();
constexpr std::make_unsigned_t<DiffT> size() const;
// [range.any.swap]
constexpr void swap(any_view&) noexcept;
constexpr friend void swap(any_view&, any_view&) noexcept;
};
} // namespace beman::any_view
template <class ElementT, beman::any_view::any_view_options OptsV, class RefT, class RValueRefT, class DiffT>
inline constexpr bool std::ranges::enable_borrowed_range<
beman::any_view::any_view<ElementT, OptsV, RefT, RValueRefT, DiffT>> =
bool(OptsV & beman::any_view::any_view_options::borrowed);There are workflows available in CMake presets such as gcc-debug:
cmake --workflow --preset gcc-debugAlternatively you can manually configure, build, and test with CMake and CTest:
cmake -B build
cmake --build build
ctest --test-dir buildPossible output
Executing workflow step 1 of 3: configure preset "gcc-debug"
Preset CMake variables:
BEMAN_BUILDSYS_SANITIZER="MaxSan"
CMAKE_BUILD_TYPE="Debug"
CMAKE_EXPORT_COMPILE_COMMANDS:BOOL="TRUE"
CMAKE_TOOLCHAIN_FILE="cmake/gnu-toolchain.cmake"
-- The CXX compiler identification is GNU 15.0.0
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/g++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- The C compiler identification is GNU 15.0.0
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /usr/bin/gcc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Found Python3: /usr/bin/python3.12 (found version "3.12.7") found components: Interpreter
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD - Success
-- Found Threads: TRUE
-- Configuring done (2.7s)
-- Generating done (0.0s)
-- Build files have been written to: /home/patrick/projects/any_view/build/gcc-debug
Executing workflow step 2 of 3: build preset "gcc-debug"
[12/12] Linking CXX executable tests/beman/any_view/beman.any_view.tests.constexpr
Executing workflow step 3 of 3: test preset "gcc-debug"
Test project /home/patrick/projects/any_view/build/gcc-debug
Start 1: ConceptsTest.iterator_concept
1/21 Test #1: ConceptsTest.iterator_concept ................... Passed 0.01 sec
Start 2: ConceptsTest.sized_concept
2/21 Test #2: ConceptsTest.sized_concept ...................... Passed 0.01 sec
Start 3: ConceptsTest.borrowed_concept
3/21 Test #3: ConceptsTest.borrowed_concept ................... Passed 0.01 sec
Start 4: ConceptsTest.copyable_concept
4/21 Test #4: ConceptsTest.copyable_concept ................... Passed 0.01 sec
Start 5: ConstexprTest.sum_vector_of_vector
5/21 Test #5: ConstexprTest.sum_vector_of_vector .............. Passed 0.01 sec
Start 6: ConstexprTest.sum_transform_view_of_iota_view
6/21 Test #6: ConstexprTest.sum_transform_view_of_iota_view ... Passed 0.01 sec
Start 7: ConstexprTest.sum_vector_of_iota_view
7/21 Test #7: ConstexprTest.sum_vector_of_iota_view ........... Passed 0.01 sec
Start 8: ConstexprTest.sort_vector
8/21 Test #8: ConstexprTest.sort_vector ....................... Passed 0.01 sec
Start 9: SfinaeTest.istream_view
9/21 Test #9: SfinaeTest.istream_view ......................... Passed 0.01 sec
Start 10: SfinaeTest.forward_list
10/21 Test #10: SfinaeTest.forward_list ......................... Passed 0.01 sec
Start 11: SfinaeTest.list
11/21 Test #11: SfinaeTest.list ................................. Passed 0.01 sec
Start 12: SfinaeTest.deque
12/21 Test #12: SfinaeTest.deque ................................ Passed 0.01 sec
Start 13: SfinaeTest.vector
13/21 Test #13: SfinaeTest.vector ............................... Passed 0.01 sec
Start 14: SfinaeTest.vector_of_bool
14/21 Test #14: SfinaeTest.vector_of_bool ....................... Passed 0.01 sec
Start 15: SfinaeTest.span
15/21 Test #15: SfinaeTest.span ................................. Passed 0.01 sec
Start 16: TypeTraitsTest.value_type
16/21 Test #16: TypeTraitsTest.value_type ....................... Passed 0.01 sec
Start 17: TypeTraitsTest.reference_type
17/21 Test #17: TypeTraitsTest.reference_type ................... Passed 0.01 sec
Start 18: TypeTraitsTest.rvalue_reference_type
18/21 Test #18: TypeTraitsTest.rvalue_reference_type ............ Passed 0.01 sec
Start 19: TypeTraitsTest.difference_type
19/21 Test #19: TypeTraitsTest.difference_type .................. Passed 0.01 sec
Start 20: TypeTraitsTest.size_type
20/21 Test #20: TypeTraitsTest.size_type ........................ Passed 0.01 sec
Start 21: TypeTraitsTest.borrowed_iterator_type
21/21 Test #21: TypeTraitsTest.borrowed_iterator_type ........... Passed 0.01 sec
100% tests passed, 0 tests failed out of 21
Total Test time (real) = 0.15 sec
Various benchmarks are available to build and run using the CMake target beman.any_view.benchmarks.
Example output comparing reserved to fused for beman.any_view.benchmarks.all
+ cmake --build build --config Release --target beman.any_view.benchmarks.all
[27/27] Linking CXX executable tests/beman/any_view/beman.any_view.benchmarks.all
+ build/_deps/benchmark-src/tools/compare.py benchmarksfiltered build/tests/beman/any_view/beman.any_view.benchmarks.all reserved build/tests/beman/any_view/beman.any_view.benchmarks.all fused
RUNNING: build/tests/beman/any_view/beman.any_view.benchmarks.all --benchmark_filter=reserved
Run on (32 X 2419.2 MHz CPU s)
CPU Caches:
L1 Data 48 KiB (x16)
L1 Instruction 32 KiB (x16)
L2 Unified 2048 KiB (x16)
L3 Unified 36864 KiB (x1)
Load Average: 0.25, 0.17, 0.11
-----------------------------------------------------------------
Benchmark Time CPU Iterations
-----------------------------------------------------------------
BM_all_reserved/1024 1783 ns 1783 ns 389936
BM_all_reserved/2048 3839 ns 3839 ns 191729
BM_all_reserved/4096 7067 ns 7067 ns 89826
BM_all_reserved/8192 14756 ns 14756 ns 48245
BM_all_reserved/16384 30317 ns 30317 ns 23191
BM_all_reserved/32768 73651 ns 73650 ns 9626
BM_all_reserved/65536 215342 ns 215341 ns 3413
BM_all_reserved/131072 424794 ns 424793 ns 1654
BM_all_reserved/262144 887833 ns 887828 ns 789
RUNNING: build/tests/beman/any_view/beman.any_view.benchmarks.all --benchmark_filter=fused
Run on (32 X 2419.2 MHz CPU s)
CPU Caches:
L1 Data 48 KiB (x16)
L1 Instruction 32 KiB (x16)
L2 Unified 2048 KiB (x16)
L3 Unified 36864 KiB (x1)
Load Average: 0.31, 0.19, 0.11
--------------------------------------------------------------
Benchmark Time CPU Iterations
--------------------------------------------------------------
BM_all_fused/1024 1660 ns 1660 ns 437469
BM_all_fused/2048 3219 ns 3219 ns 210096
BM_all_fused/4096 7100 ns 7100 ns 100823
BM_all_fused/8192 15088 ns 15088 ns 45117
BM_all_fused/16384 33719 ns 33719 ns 21827
BM_all_fused/32768 72098 ns 72097 ns 9582
BM_all_fused/65536 150699 ns 150698 ns 4629
BM_all_fused/131072 316431 ns 316430 ns 2234
BM_all_fused/262144 583499 ns 583500 ns 1091
Comparing reserved (from build/tests/beman/any_view/beman.any_view.benchmarks.all) to fused (from build/tests/beman/any_view/beman.any_view.benchmarks.all)
Benchmark Time CPU Time Old Time New CPU Old CPU New
---------------------------------------------------------------------------------------------------------------------------------
BM_all_[reserved vs. fused]/1024 -0.0689 -0.0689 1783 1660 1783 1660
BM_all_[reserved vs. fused]/2048 -0.1615 -0.1615 3839 3219 3839 3219
BM_all_[reserved vs. fused]/4096 +0.0047 +0.0047 7067 7100 7067 7100
BM_all_[reserved vs. fused]/8192 +0.0225 +0.0225 14756 15088 14756 15088
BM_all_[reserved vs. fused]/16384 +0.1122 +0.1122 30317 33719 30317 33719
BM_all_[reserved vs. fused]/32768 -0.0211 -0.0211 73651 72098 73650 72097
BM_all_[reserved vs. fused]/65536 -0.3002 -0.3002 215342 150699 215341 150698
BM_all_[reserved vs. fused]/131072 -0.2551 -0.2551 424794 316431 424793 316430
BM_all_[reserved vs. fused]/262144 -0.3428 -0.3428 887833 583499 887828 583500
OVERALL_GEOMEAN -0.1255 -0.1255
Please do! Issues and pull requests are appreciated.