Implements `begin()` / `end()` utility functions for ranges in C++17 and C++20 #2493

SergeyKopienko · 2025-10-07T16:10:05Z

This PR implements some new utility functions for handling ranges in both C++17 and C++20 environments, providing a unified interface for accessing range iterators:

oneapi::dpl::__ranges::__begin()
oneapi::dpl::__ranges::__end()

The implementation uses C++20's std::ranges API when available and falls back to trait-based detection for C++17.

Added oneapi::dpl::__ranges::__begin() and oneapi::dpl::__ranges::__end() utility functions with conditional compilation for C++17/C++20
Introduced __iterator_t type alias for consistent iterator type handling
Updated existing code to use the new utilities instead of direct method calls

Also in this PR some functions has been refactored and simplified:

oneapi::dpl::__ranges::__size()
oneapi::dpl::__ranges::__empty()

Copilot

Pull Request Overview

This PR implements utility functions __begin() and __end() for handling ranges in both C++17 and C++20 environments, providing a unified interface for accessing range iterators. The implementation uses C++20's std::ranges API when available and falls back to trait-based detection for C++17.

Added __begin() and __end() utility functions with conditional compilation for C++17/C++20
Introduced __iterator_t type alias for consistent iterator type handling
Updated existing code to use the new utilities instead of direct method calls

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
include/oneapi/dpl/pstl/utils_ranges.h	Implements the core `__begin()`/`__end()` utilities and updates existing functions to use them
include/oneapi/dpl/pstl/hetero/algorithm_ranges_impl_hetero.h	Updates iterator type extraction to use new `__iterator_t` alias

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include/oneapi/dpl/pstl/utils_ranges.h

…oneapi::dpl::__ranges::__begin() / oneapi::dpl::__ranges::__end() methods

… ranges

…ranges::__empty() method based on oneapi::dpl::__ranges::__begin() and oneapi::dpl::__ranges::__end() methods

…ranges::__size() method based on oneapi::dpl::__ranges::__begin() and oneapi::dpl::__ranges::__end() methods

…:__begin() in struct __subscription_impl_view_simple::operator[]

… oneapi::dpl::__ranges::__iterator_t in __pattern_min_element_impl + _BackendTag

… oneapi::dpl::__ranges::__iterator_t in __pattern_minmax_element_impl + _BackendTag

…internal::__value_t based on oneapi::dpl::__ranges::__iterator_t

…:dpl::__internal::__value_t based on oneapi::dpl::__ranges::__iterator_t" This reverts commit 56a1c26.

… / end() methods through ADL

… / end() methods for arrays

…__ranges::__begin() / oneapi::dpl::__ranges::__end() methods

…e _IteratorValueType through oneapi::dpl::__ranges::__iterator_t<_Range> in __pattern_min_element_impl + _BackendTag and __pattern_minmax_element_impl + _BackendTag methods

…terator_t as not used anymore

…ace before __begin() calls

…ienko/avoid_begin_end_calls_for_ranges

…f namespace before __begin() calls" This reverts commit 0b445fa.

…ace before __begin() calls

…et_count() method call to __get_buffer_size() call In file included from /oneDPL/oneDPL/test/parallel_api/ranges/adjacent_find_ranges_sycl.pass.cpp:18: In file included from /oneDPL/oneDPL/include/oneapi/dpl/execution:70: In file included from /oneDPL/oneDPL/include/oneapi/dpl/pstl/algorithm_impl.h:28: In file included from /oneDPL/oneDPL/include/oneapi/dpl/pstl/execution_impl.h:22: In file included from /oneDPL/oneDPL/include/oneapi/dpl/pstl/parallel_backend.h:32: In file included from /oneDPL/oneDPL/include/oneapi/dpl/pstl/hetero/dpcpp/parallel_backend_sycl.h:34: /oneDPL/oneDPL/include/oneapi/dpl/pstl/hetero/dpcpp/../../utils_ranges.h:187:51: error: 'get_count' is deprecated: get_count() is deprecated, please use size() instead [-Werror,-Wdeprecated-declarations] 187 | __check_size(int) -> decltype(std::declval<_R&>().get_count()); | ^ /oneDPL/oneDPL/include/oneapi/dpl/pstl/hetero/dpcpp/../../utils_ranges.h:208:52: note: while substituting explicitly-specified template arguments into function template '__check_size' 208 | using __difference_t = std::make_signed_t<decltype(__check_size<_R>(0))>; | ^ /oneDPL/oneDPL/include/oneapi/dpl/pstl/glue_algorithm_ranges_impl.h:1473:98: note: in instantiation of template type alias '__difference_t' requested here 1473 | oneapi::dpl::__internal::__enable_if_execution_policy<_ExecutionPolicy, oneapi::dpl::__internal::__difference_t<_Range>> | ^ /oneDPL/oneDPL/test/parallel_api/ranges/adjacent_find_ranges_sycl.pass.cpp:46:16: note: while substituting deduced template arguments into function template 'adjacent_find' [with _ExecutionPolicy = const oneapi::dpl::execution::device_policy<> &, _Range = sycl::buffer<int> &, _BinaryPredicate = TestUtils::IsEqual<int>] 46 | res2 = adjacent_find(CLONE_TEST_POLICY_IDX(exec, 1), A, TestUtils::IsEqual<int>()); | ^ /oneDPL/oneDPL/test/parallel_api/ranges/adjacent_find_ranges_sycl.pass.cpp:61:5: note: in instantiation of function template specialization 'test_impl<oneapi::dpl::execution::device_policy<> &>' requested here 61 | test_impl(policy); | ^ /opt/intel/oneapi/compiler/2025.2/bin/compiler/../../include/sycl/buffer.hpp:497:3: note: 'get_count' has been explicitly marked deprecated here 497 | __SYCL2020_DEPRECATED("get_count() is deprecated, please use size() instead") | ^ /opt/intel/oneapi/compiler/2025.2/bin/compiler/../../include/sycl/detail/defines_elementary.hpp:62:40: note: expanded from macro '__SYCL2020_DEPRECATED' 62 | #define __SYCL2020_DEPRECATED(message) __SYCL_DEPRECATED(message) | ^ /opt/intel/oneapi/compiler/2025.2/bin/compiler/../../include/sycl/detail/defines_elementary.hpp:53:38: note: expanded from macro '__SYCL_DEPRECATED' 53 | #define __SYCL_DEPRECATED(message) [[deprecated(message)]] | ^

SergeyKopienko · 2025-10-10T12:05:20Z

include/oneapi/dpl/pstl/utils_ranges.h


 template <typename _R>
 auto
-__check_size(long) -> decltype(std::declval<_R&>().get_count());


I have changed this line to avoid compile error like described in the message for commit ba01762

Now it's implemented as

template <typename _R> auto __check_size(int) -> decltype(__get_buffer_size(std::declval<_R&>()));

SergeyKopienko · 2025-10-10T12:23:29Z

include/oneapi/dpl/pstl/utils_ranges.h

+#if _ONEDPL_CPP20_RANGES_PRESENT
+template <typename _Range>
+auto
+__size(_Range&& __rng) -> decltype(std::ranges::size(__rng))


We should declare return type here as -> decltype(std::ranges::size(__rng)) because we using this function __size() now in

template <typename _R> auto __check_size(long) -> decltype(oneapi::dpl::__ranges::__size(std::declval<_R&>()));

SergeyKopienko · 2025-10-10T12:46:13Z

include/oneapi/dpl/pstl/utils_ranges.h

-template <typename _It>
+template <typename _R>
 auto
-__check_size(...) -> typename std::iterator_traits<_It>::difference_type;


Now re doing the same task in

auto __check_size(long long) -> typename std::iterator_traits<_It>::difference_type;

SergeyKopienko · 2025-10-10T12:46:43Z

include/oneapi/dpl/pstl/utils_ranges.h

-__check_size(...) -> typename std::iterator_traits<_It>::difference_type;
+__check_size(...)
+{
+    //static_assert should always fail when this overload is chosen, so its condition must depend on


And here we have compile error if something were not compiled (__check_size return type not evaluated).
This helps us to understand in which type we have the problem.

danhoeflinger

LGTM after changes

test/support/utils.h

…ize() for struct MinimalisticRange

…) / size() implementations

…nge<ForwardIterator>) function as not required

…declaration for __begin(_Range&& __rng)

dmitriy-sobolev

LGTM. Could you wait for the CI to pass before merging?

…libc++ 18 and older

…ix run-time errors

…or>), end(MinimalisticRange<ForwardIterator>)

akukanov · 2025-10-13T12:55:43Z

test/parallel_api/ranges/range_minimal_type_requirements.pass.cpp

+    else
+    {
+        return std::vector<int, typename sycl::usm_allocator<int, sycl::usm::alloc::shared>>(
+            typename sycl::usm_allocator<int, sycl::usm::alloc::shared>(policy.queue()));
+    }


Apparently keeping this SYCL-dependent code under the if constexpr condition is not sufficient - it still requires having SYCL API available, which leads to test failures. Looks like either checking a macro or some SFINAE dispatch is needed.

MikeDvorskiy · 2025-10-13T16:25:11Z

include/oneapi/dpl/pstl/utils_ranges.h

+                 decltype(std::distance(__begin(std::declval<_Range>()), __end(std::declval<_Range>())))>
+__size(_Range&& __rng)
+{
+    return std::distance(__begin(__rng), __end(__rng));


I would like to issue a note of caution here, because it might affect perfomance.
Usually a size() method of C++ library types "Calculates the number of elements in t in constant time."
It is true for the ranges as well. I see that it is an internal function __size, but.. in any case the semantic and complexity should be the same, I believe.

Disagree. Please take a look to around code, this code will works in case when the range passed into this function doesn't support .size() method.

Mikhail says that this overload cannot guarantee that the distance is computed in O(1), which impacts the overall complexity guarantee of __size - unlike std::ranges::size, this function does not generally guarantee constant time. That's a fair point.

However, complexity of the method size() (as well as of std::size) might depend on a particular container - it is usually constant time, but that is not guaranteed. So technically this overload does not make it worse.

For me, the question is whether we have added this overload just in case or it is known to be necessary in certain supported scenarios.

I added this overload to be compliant with begin() / end() methods which may be found for user range trough ADL.
For example, we are ready to use MinimalisticRange without size() method.
And we have a lot of code which need to know range size and has been written not under _ONEDPL_CPP20_RANGES_PRESENT macro.

@SergeyKopienko, let me ask a "naive" question. Why do we need to call "__size()" function with an unsized range?

If you want (or a user wants) to call "size" function with an unsized range, that means you might have wrong (not effective) implementation or code design.

A quote from cppreference:
"ranges::sized_range(C++20) | specifies that a range knows its size in constant time"

might depend on a particular container - it is usually constant time, but that is not guaranteed

@akukanov, If we are talking about C++ standard containers... do you know which containers (excepting std::list and std::basic_string before C++11) have non-constant time for "size" metod? I've checked it.. Starting from C++11 there is a "constant time" complexity requirement for the all containers, which have method size.

(https://en.cppreference.com/w/Talk%253Acpp/named_req/Container.html)
(https://en.cppreference.com/w/cpp/container/list/size.html)
(https://en.cppreference.com/w/cpp/string/basic_string/size.html)

Starting from C++11 there is a "constant time" complexity requirement for the all containers, which have method size.

Thanks for the link - I did not know the standard requirement for a "Container" guarantees constant complexity for .size(). We can also say that the containers of interest (i.e., those with random access) do not do the linear search.

But then, std::distance also guarantees constant complexity for random access iterators. Should we additionally constrain the overload by decltype(__begin(std::declval<_Range>()) being a random access iterator?

…ix review comment

SergeyKopienko added enhancement bug labels Oct 7, 2025

SergeyKopienko added this to the 2022.11.0 milestone Oct 7, 2025

SergeyKopienko requested a review from Copilot October 7, 2025 16:10

Copilot AI reviewed Oct 7, 2025

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SergeyKopienko added 21 commits October 8, 2025 11:04

test/support/utils.h - fix compile error in struct MinimalisticRange

4b4452d

include/oneapi/dpl/pstl/utils_ranges.h - implementation of universal …

c1c7fa8

…oneapi::dpl::__ranges::__begin() / oneapi::dpl::__ranges::__end() methods

include/oneapi/dpl/pstl/utils_ranges.h - insert additional comments

095dead

include/oneapi/dpl/pstl/utils_ranges.h - define __iterator_t type for…

8f01d1d

… ranges

include/oneapi/dpl/pstl/utils_ranges.h - re-implement oneapi::dpl::__…

659ffeb

…ranges::__empty() method based on oneapi::dpl::__ranges::__begin() and oneapi::dpl::__ranges::__end() methods

include/oneapi/dpl/pstl/utils_ranges.h - re-implement oneapi::dpl::__…

d8cd950

…ranges::__size() method based on oneapi::dpl::__ranges::__begin() and oneapi::dpl::__ranges::__end() methods

include/oneapi/dpl/pstl/utils_ranges.h - apply oneapi::dpl::__ranges:…

83462de

…:__begin() in struct __subscription_impl_view_simple::operator[]

include/oneapi/dpl/pstl/hetero/algorithm_ranges_impl_hetero.h - apply…

56db3b4

… oneapi::dpl::__ranges::__iterator_t in __pattern_min_element_impl + _BackendTag

include/oneapi/dpl/pstl/hetero/algorithm_ranges_impl_hetero.h - apply…

9b70191

… oneapi::dpl::__ranges::__iterator_t in __pattern_minmax_element_impl + _BackendTag

include/oneapi/dpl/pstl/utils_ranges.h - re-implement oneapi::dpl::__…

ea5a684

…internal::__value_t based on oneapi::dpl::__ranges::__iterator_t

Revert "include/oneapi/dpl/pstl/utils_ranges.h - re-implement oneapi:…

e433702

…:dpl::__internal::__value_t based on oneapi::dpl::__ranges::__iterator_t" This reverts commit 56a1c26.

include/oneapi/dpl/pstl/utils_ranges.h - remove try to lookup begin()…

b4ca0c9

… / end() methods through ADL

include/oneapi/dpl/pstl/utils_ranges.h - remove try to lookup begin()…

4309083

… / end() methods for arrays

include/oneapi/dpl/pstl/utils_ranges.h - fix compile errors

435f5b4

include/oneapi/dpl/pstl/utils_ranges.h - fix review comment

fb22a88

include/oneapi/dpl/pstl/utils_ranges.h - refactoring of oneapi::dpl::…

d912ec8

…__ranges::__begin() / oneapi::dpl::__ranges::__end() methods

include/oneapi/dpl/pstl/hetero/algorithm_ranges_impl_hetero.h - defin…

a3b51b7

…e _IteratorValueType through oneapi::dpl::__ranges::__iterator_t<_Range> in __pattern_min_element_impl + _BackendTag and __pattern_minmax_element_impl + _BackendTag methods

include/oneapi/dpl/pstl/utils_ranges.h - remove the definition of __i…

42ce3ba

…terator_t as not used anymore

include/oneapi/dpl/pstl/utils_ranges.h - remove extra names of namesp…

0b445fa

…ace before __begin() calls

include/oneapi/dpl/pstl/utils_ranges.h - remove extra comments

6c0d832

include/oneapi/dpl/pstl/utils_ranges.h - fix compile error

d9b5da0

SergeyKopienko force-pushed the dev/skopienko/avoid_begin_end_calls_for_ranges branch from 9dbcd3c to d9b5da0 Compare October 8, 2025 09:08

SergeyKopienko added 3 commits October 8, 2025 11:08

Merge branch 'dev/skopienko/fix_compile_error_in_tests' into dev/skop…

5196ffd

…ienko/avoid_begin_end_calls_for_ranges

Revert "include/oneapi/dpl/pstl/utils_ranges.h - remove extra names o…

79b55d0

…f namespace before __begin() calls" This reverts commit 0b445fa.

include/oneapi/dpl/pstl/utils_ranges.h - remove extra names of namesp…

04b78fe

…ace before __begin() calls

SergeyKopienko requested a review from dmitriy-sobolev October 10, 2025 11:50

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test/support/utils.h - rewrite implementations of begin() / end() / s…

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…ize() for struct MinimalisticRange

SergeyKopienko dismissed danhoeflinger’s stale review via fc1bf0b October 10, 2025 15:48

include/oneapi/dpl/pstl/utils_ranges.h - fix errors in begin() / end(…

5f6ec53

…) / size() implementations

SergeyKopienko force-pushed the dev/skopienko/avoid_begin_end_calls_for_ranges branch from fc1bf0b to 5f6ec53 Compare October 13, 2025 07:56

test/support/utils.h - fix review comment: remove size(MinimalisticRa…

34bcadc

…nge<ForwardIterator>) function as not required

SergeyKopienko requested review from danhoeflinger and dmitriy-sobolev October 13, 2025 08:03

SergeyKopienko added 2 commits October 13, 2025 10:08

include/oneapi/dpl/pstl/utils_ranges.h - fix an error in output type …

e55b1e2

…declaration for __begin(_Range&& __rng)

Merge branch 'main' into dev/skopienko/avoid_begin_end_calls_for_ranges

d6bc7cc

dmitriy-sobolev previously approved these changes Oct 13, 2025

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test/support/utils.h - fix compile error for libstdc++ 13 and older, …

78617e0

…libc++ 18 and older

SergeyKopienko dismissed dmitriy-sobolev’s stale review via 78617e0 October 13, 2025 09:35

SergeyKopienko added 2 commits October 13, 2025 12:44

test/parallel_api/ranges/range_minimal_type_requirements.pass.cpp - f…

1b1e2f4

…ix run-time errors

test/support/utils.h - simplify begin(MinimalisticRange<ForwardIterat…

73d67b6

…or>), end(MinimalisticRange<ForwardIterator>)

SergeyKopienko force-pushed the dev/skopienko/avoid_begin_end_calls_for_ranges branch from 6362e53 to 73d67b6 Compare October 13, 2025 11:27

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test/parallel_api/ranges/range_minimal_type_requirements.pass.cpp - f…

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…ix review comment

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SergeyKopienko added 2 commits October 15, 2025 11:33

@@@

1a49f7d

@@@

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SergeyKopienko force-pushed the dev/skopienko/avoid_begin_end_calls_for_ranges branch from 8de3893 to 0334bea Compare October 15, 2025 10:06

Implements __begin() / __end() utility functions for ranges in C++17 and C++20 #2493

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Implements __begin() / __end() utility functions for ranges in C++17 and C++20 #2493

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Implements `begin()` / `end()` utility functions for ranges in C++17 and C++20 #2493

Implements `begin()` / `end()` utility functions for ranges in C++17 and C++20 #2493

SergeyKopienko commented Oct 7, 2025 •

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