Make <string_view> slimmer by default
#4633
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The new header `<__msvc_string_view.hpp>` provides `char_traits` and `basic_string_view` and related utilities. `<string_view>` shouldn't provide other utilities in `<xstring>`. `<ranges>` seemingly still need to include `<xmemory>` in C++23 due to `elements_of` whose default template argument depends on `allocator`. Escape hatch `_LEGACY_CODE_ASSUMES_STRING_VIEW_INCLUDES_XSTRING` is added to restore legacy inclusion. MSVC-internal changes are needed due to the new internal header.
StephanTLavavej
approved these changes
May 29, 2024
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Thanks - I pushed a conflict-free merge with |
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I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed. |
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Thanks for this significant throughput improvement for people who are carefully including only |
7 tasks
This was referenced Jun 6, 2024
kou
pushed a commit
to apache/arrow
that referenced
this pull request
Jun 7, 2024
### Rationale for this change I work on MSVC's STL, and we regularly build popular open-source projects, including yours, with development builds of the MSVC toolset. This allows us to find and fix toolset regressions before they affect users, and also allows us to provide advance notice of breaking changes, which is the case here. We recently merged microsoft/STL#4633 which will ship in VS 2022 17.11 Preview 3. This improved build throughput by refactoring `<string_view>` so that it no longer drags in `std::string`. It's also a source-breaking change for code that wasn't properly including `<string>`. Your `cpp/src/arrow/json/object_writer.h` declares `std::string Serialize();` without including `<string>`. When built with our updated STL, this will emit a compiler error: ``` C:\gitP\apache\arrow\cpp\src\arrow/json/object_writer.h(39): error C2039: 'string': is not a member of 'std' ``` ### What changes are included in this PR? The fix is simple and portable: include the necessary header. ### Are these changes tested? Nope, I'm totally YOLOing it. If it builds, it's good. (This will be tested in MSVC's internal "Real World Code" test infrastructure. Also, after VS 2022 17.11 ships, your existing build/test coverage will ensure that this keeps compiling.) ### Are there any user-facing changes? No. Authored-by: Stephan T. Lavavej <stl@microsoft.com> Signed-off-by: Sutou Kouhei <kou@clear-code.com>
This was referenced Jun 7, 2024
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The new header
<__msvc_string_view.hpp>provideschar_traitsandbasic_string_viewand related utilities.<string_view>shouldn't provide other utilities in<xstring>. Fixes #4625.<ranges>seemingly still need to include<xmemory>in C++23 due toelements_ofwhose default template argument depends onallocator(see #4620).Escape hatch
_LEGACY_CODE_ASSUMES_STRING_VIEW_INCLUDES_XSTRINGis provided to restore legacy inclusion.MSVC-internal changes are needed due to the new internal header.