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libstdc++: Add __maybe_const_t and __maybe_empty_t aliases

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This introduces a couple of convenience alias templates to be used for
some repeated patterns using std::conditional_t.

	* include/std/ranges (__detail::__maybe_empty_t): Define new helper
	alias.
	(__detail::__maybe_const_t): Likewise.
	(__adaptor::_RangeAdaptor): Use __maybe_empty_t.
	(transform_view, take_view, take_while_view, elements_view): Use
	__maybe_const_t.
	(join_view, split_view): Use both.
This commit is contained in:
Jonathan Wakely 2020-02-26 15:19:43 +00:00
parent 4a305fa2fd
commit 8017d95c7f
2 changed files with 39 additions and 24 deletions
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10
libstdc++-v3/ChangeLog
View File

@ -1,3 +1,13 @@
2020-02-26 Jonathan Wakely <jwakely@redhat.com>
* include/std/ranges (__detail::__maybe_empty_t): Define new helper
alias.
(__detail::__maybe_const_t): Likewise.
(__adaptor::_RangeAdaptor): Use __maybe_empty_t.
(transform_view, take_view, take_while_view, elements_view): Use
__maybe_const_t.
(join_view, split_view): Use both.
2020-02-25 Patrick Palka <ppalka@redhat.com>
LWG 3397 basic_istream_view::iterator should not provide

53
libstdc++-v3/include/std/ranges
View File

@ -1029,6 +1029,13 @@ namespace views
namespace __detail
{
struct _Empty { };
template<bool _NonEmpty, typename _Tp>
using __maybe_empty_t = conditional_t<_NonEmpty, _Tp, _Empty>;
template<bool _Const, typename _Tp>
using __maybe_const_t = conditional_t<_Const, const _Tp, _Tp>;
} // namespace __detail
namespace views
@ -1058,8 +1065,8 @@ namespace views
{
protected:
[[no_unique_address]]
conditional_t<!is_default_constructible_v<_Callable>,
_Callable, __detail::_Empty> _M_callable;
__detail::__maybe_empty_t<!is_default_constructible_v<_Callable>,
_Callable> _M_callable;
public:
constexpr
@ -1552,9 +1559,8 @@ namespace views
struct _Iterator
{
private:
using _Parent
= conditional_t<_Const, const transform_view, transform_view>;
using _Base = conditional_t<_Const, const _Vp, _Vp>;
using _Parent = __detail::__maybe_const_t<_Const, transform_view>;
using _Base = __detail::__maybe_const_t<_Const, _Vp>;
static constexpr auto
_S_iter_concept()
@ -1760,9 +1766,8 @@ namespace views
struct _Sentinel
{
private:
using _Parent
= conditional_t<_Const, const transform_view, transform_view>;
using _Base = conditional_t<_Const, const _Vp, _Vp>;
using _Parent = __detail::__maybe_const_t<_Const, transform_view>;
using _Base = __detail::__maybe_const_t<_Const, _Vp>;
constexpr range_difference_t<_Base>
__distance_from(const _Iterator<_Const>& __i) const
@ -1886,7 +1891,7 @@ namespace views
struct _Sentinel
{
private:
using _Base = conditional_t<_Const, const _Vp, _Vp>;
using _Base = __detail::__maybe_const_t<_Const, _Vp>;
using _CI = counted_iterator<iterator_t<_Base>>;
sentinel_t<_Base> _M_end = sentinel_t<_Base>();
@ -2025,7 +2030,7 @@ namespace views
struct _Sentinel
{
private:
using _Base = conditional_t<_Const, const _Vp, _Vp>;
using _Base = __detail::__maybe_const_t<_Const, _Vp>;
sentinel_t<_Base> _M_end = sentinel_t<_Base>();
const _Pred* _M_pred = nullptr;
@ -2258,8 +2263,8 @@ namespace views
struct _Iterator
{
private:
using _Parent = conditional_t<_Const, const join_view, join_view>;
using _Base = conditional_t<_Const, const _Vp, _Vp>;
using _Parent = __detail::__maybe_const_t<_Const, join_view>;
using _Base = __detail::__maybe_const_t<_Const, _Vp>;
static constexpr bool _S_ref_is_glvalue
= is_reference_v<range_reference_t<_Base>>;
@ -2450,8 +2455,8 @@ namespace views
struct _Sentinel
{
private:
using _Parent = conditional_t<_Const, const join_view, join_view>;
using _Base = conditional_t<_Const, const _Vp, _Vp>;
using _Parent = __detail::__maybe_const_t<_Const, join_view>;
using _Base = __detail::__maybe_const_t<_Const, _Vp>;
constexpr bool
__equal(const _Iterator<_Const>& __i) const
@ -2482,8 +2487,8 @@ namespace views
// XXX: _M_inner is "present only when !is_reference_v<_InnerRange>"
[[no_unique_address]]
conditional_t<!is_reference_v<_InnerRange>,
views::all_t<_InnerRange>, __detail::_Empty> _M_inner;
__detail::__maybe_empty_t<!is_reference_v<_InnerRange>,
views::all_t<_InnerRange>> _M_inner;
public:
join_view() = default;
@ -2585,8 +2590,8 @@ namespace views
struct _OuterIter
{
private:
using _Parent = conditional_t<_Const, const split_view, split_view>;
using _Base = conditional_t<_Const, const _Vp, _Vp>;
using _Parent = __detail::__maybe_const_t<_Const, split_view>;
using _Base = __detail::__maybe_const_t<_Const, _Vp>;
constexpr bool
__at_end() const
@ -2618,8 +2623,8 @@ namespace views
// XXX: _M_current is present only if "V models forward_range"
[[no_unique_address]]
conditional_t<forward_range<_Vp>,
iterator_t<_Base>, __detail::_Empty> _M_current;
__detail::__maybe_empty_t<forward_range<_Vp>,
iterator_t<_Base>> _M_current;
public:
using iterator_concept = conditional_t<forward_range<_Base>,
@ -2732,7 +2737,7 @@ namespace views
struct _InnerIter
{
private:
using _Base = conditional_t<_Const, const _Vp, _Vp>;
using _Base = __detail::__maybe_const_t<_Const, _Vp>;
constexpr bool
__at_end() const
@ -2858,8 +2863,8 @@ namespace views
// XXX: _M_current is "present only if !forward_range<V>"
[[no_unique_address]]
conditional_t<!forward_range<_Vp>,
iterator_t<_Vp>, __detail::_Empty> _M_current;
__detail::__maybe_empty_t<!forward_range<_Vp>, iterator_t<_Vp>>
_M_current;
public:
@ -3223,7 +3228,7 @@ namespace views
template<bool _Const>
struct _Iterator
{
using _Base = conditional_t<_Const, const _Vp, _Vp>;
using _Base = __detail::__maybe_const_t<_Const, _Vp>;
iterator_t<_Base> _M_current = iterator_t<_Base>();