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Support For Incomplete Types In reference_wrapper #393

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Merged
Billy O'Neal (BillyONeal) merged 6 commits into from
Jan 9, 2020
Merged

Support For Incomplete Types In reference_wrapper #393

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e3c45e5
Merge pull request #2 from microsoft/master
AdamBucior Dec 5, 2019
0b0d96d
Implement P0357R3
AdamBucior Dec 17, 2019
5dd7e79
Merge remote-tracking branch 'origin/master' into ref-wrapper-incompl…
BillyONeal Dec 17, 2019
b65e367
Remove meaningless comment
AdamBucior Dec 17, 2019
f01cf25
Merge remote-tracking branch 'origin/master' into ref-wrapper-incompl…
BillyONeal Jan 8, 2020
a8f0f5b
Update LLVM to get skip of libcxx\test\std\utilities\function.objects…
BillyONeal Jan 9, 2020
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2 changes: 1 addition & 1 deletion llvm-project
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Submodule llvm-project updated 4817 files
6 changes: 5 additions & 1 deletion stl/inc/type_traits
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Original file line number Diff line number Diff line change
Expand Up @@ -1845,7 +1845,11 @@ template <class _Ty, class _Uty>
struct _Refwrap_has_ctor_from<_Ty, _Uty, void_t<decltype(_Refwrap_ctor_fun<_Ty>(_STD declval<_Uty>()))>> : true_type {};

template <class _Ty>
class reference_wrapper : public _Weak_types<_Ty>::type { // stand-in for an assignable reference
class reference_wrapper
#if !_HAS_CXX20
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BillyONeal marked this conversation as resolved.
: public _Weak_types<_Ty>::type

@StephanTLavavej Stephan T. Lavavej (StephanTLavavej) Jan 9, 2020

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There's a design question here, because we haven't yet merged #380 to implement #28 (WG21-P0619 Removing C++17-Deprecated Features In C++20). Specifically, an escape hatch to restore reference_wrapper's weak result type is incompatible with supporting incomplete types. There are two possible decisions: allow reference_wrapper to be affected by such an escape hatch (thereby disabling support for incomplete types), or exempt reference_wrapper from the escape hatch (so C++20 mode always activates support for incomplete types).

It's not a big deal because reference_wrapper's support for weak result types is extremely obscure. I am inclined to accept the code as-is, meaning that C++20 mode always makes reference_wrapper support incomplete types and removes its weak result type, even if weak result types have otherwise been escape-hatched.

#endif // !_HAS_CXX20
{
public:
static_assert(is_object_v<_Ty> || is_function_v<_Ty>,
"reference_wrapper<T> requires T to be an object type or a function type.");
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1 change: 1 addition & 0 deletions stl/inc/yvals_core.h
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Expand Up @@ -130,6 +130,7 @@
// P0318R1 unwrap_reference, unwrap_ref_decay
// P0325R4 to_array()
// P0356R5 bind_front()
// P0357R3 Supporting Incomplete Types In reference_wrapper
// P0439R0 enum class memory_order
// P0457R2 starts_with()/ends_with() For basic_string/basic_string_view
// P0458R2 contains() For Ordered And Unordered Associative Containers
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1 change: 1 addition & 0 deletions tests/libcxx/magic_comments.txt
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Expand Up @@ -2,4 +2,5 @@
// REQUIRES: c++11 || c++14
// REQUIRES: c++98 || c++03
// REQUIRES: c++98 || c++03 || c++11 || c++14
// REQUIRES: c++98 || c++03 || c++11 || c++14 || c++17
// UNSUPPORTED: c++14, c++17, c++2a