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[libcxx][span] Implement solution to LWG-3255 

This implements the relaxed requirements on the std::array constructors of span,
where the type only needs to be convertible to the element type of the span.

Note that the previous tests were not sufficient, as the const array<T, n> constructor
was only tested for compile time and the array<T, N> only during runtime.

Restructure the tests so that we can test conversions as well as both constructors.

Differential Revision: https://reviews.llvm.org/D75706
This commit is contained in:
Michael Schellenberger Costa 2020-05-14 10:50:03 -04:00 committed by Louis Dionne
parent ce4ebc14a8
commit ab9f11168f
3 changed files with 56 additions and 37 deletions
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22
libcxx/include/span
View File

@ -212,8 +212,16 @@ public:
{ (void)__l; _LIBCPP_ASSERT(_Extent == distance(__f, __l), "size mismatch in span's constructor (ptr, ptr)"); }
_LIBCPP_INLINE_VISIBILITY constexpr span(element_type (&__arr)[_Extent]) noexcept : __data{__arr} {}
_LIBCPP_INLINE_VISIBILITY constexpr span( array<value_type, _Extent>& __arr) noexcept : __data{__arr.data()} {}
_LIBCPP_INLINE_VISIBILITY constexpr span(const array<value_type, _Extent>& __arr) noexcept : __data{__arr.data()} {}
template <class _OtherElementType,
enable_if_t<is_convertible_v<_OtherElementType(*)[], element_type (*)[]>, nullptr_t> = nullptr>
_LIBCPP_INLINE_VISIBILITY
constexpr span(array<_OtherElementType, _Extent>& __arr) noexcept : __data{__arr.data()} {}
template <class _OtherElementType,
enable_if_t<is_convertible_v<const _OtherElementType(*)[], element_type (*)[]>, nullptr_t> = nullptr>
_LIBCPP_INLINE_VISIBILITY
constexpr span(const array<_OtherElementType, _Extent>& __arr) noexcept : __data{__arr.data()} {}
template <class _Container>
_LIBCPP_INLINE_VISIBILITY
@ -386,13 +394,15 @@ public:
_LIBCPP_INLINE_VISIBILITY
constexpr span(element_type (&__arr)[_Sz]) noexcept : __data{__arr}, __size{_Sz} {}
template <size_t _Sz>
template <class _OtherElementType, size_t _Sz,
enable_if_t<is_convertible_v<_OtherElementType(*)[], element_type (*)[]>, nullptr_t> = nullptr>
_LIBCPP_INLINE_VISIBILITY
constexpr span(array<value_type, _Sz>& __arr) noexcept : __data{__arr.data()}, __size{_Sz} {}
constexpr span(array<_OtherElementType, _Sz>& __arr) noexcept : __data{__arr.data()}, __size{_Sz} {}
template <size_t _Sz>
template <class _OtherElementType, size_t _Sz,
enable_if_t<is_convertible_v<const _OtherElementType(*)[], element_type (*)[]>, nullptr_t> = nullptr>
_LIBCPP_INLINE_VISIBILITY
constexpr span(const array<value_type, _Sz>& __arr) noexcept : __data{__arr.data()}, __size{_Sz} {}
constexpr span(const array<_OtherElementType, _Sz>& __arr) noexcept : __data{__arr.data()}, __size{_Sz} {}
template <class _Container>
_LIBCPP_INLINE_VISIBILITY

69
libcxx/test/std/containers/views/span.cons/stdarray.pass.cpp
View File

@ -68,49 +68,58 @@ void checkCV()
}
}
template <typename T>
constexpr bool testConstexprSpan()
template <typename T, typename U = T>
constexpr bool testConstructorArray()
{
constexpr std::array<T,2> val = { T(), T() };
ASSERT_NOEXCEPT(std::span<const T> {val});
ASSERT_NOEXCEPT(std::span<const T, 2>{val});
std::span<const T> s1{val};
std::span<const T, 2> s2{val};
return
s1.data() == &val[0] && s1.size() == 2
&& s2.data() == &val[0] && s2.size() == 2;
}
template <typename T>
void testRuntimeSpan()
{
std::array<T,2> val;
std::array<U,2> val = { U(), U() };
ASSERT_NOEXCEPT(std::span<T> {val});
ASSERT_NOEXCEPT(std::span<T, 2>{val});
std::span<T> s1{val};
std::span<T, 2> s2{val};
assert(s1.data() == &val[0] && s1.size() == 2);
assert(s2.data() == &val[0] && s2.size() == 2);
return s1.data() == &val[0] && s1.size() == 2
&& s2.data() == &val[0] && s2.size() == 2;
}
template <typename T, typename U = T>
constexpr bool testConstructorConstArray()
{
const std::array<U,2> val = { U(), U() };
ASSERT_NOEXCEPT(std::span<const T> {val});
ASSERT_NOEXCEPT(std::span<const T, 2>{val});
std::span<const T> s1{val};
std::span<const T, 2> s2{val};
return s1.data() == &val[0] && s1.size() == 2
&& s2.data() == &val[0] && s2.size() == 2;
}
template <typename T>
constexpr bool testConstructors() {
static_assert(testConstructorArray<T>(), "");
static_assert(testConstructorArray<const T, T>(), "");
static_assert(testConstructorConstArray<T>(), "");
static_assert(testConstructorConstArray<const T, T>(), "");
return testConstructorArray<T>()
&& testConstructorArray<const T, T>()
&& testConstructorConstArray<T>()
&& testConstructorConstArray<const T, T>();
}
struct A{};
int main(int, char**)
{
static_assert(testConstexprSpan<int>(), "");
static_assert(testConstexprSpan<long>(), "");
static_assert(testConstexprSpan<double>(), "");
static_assert(testConstexprSpan<A>(), "");
assert(testConstructors<int>());
assert(testConstructors<long>());
assert(testConstructors<double>());
assert(testConstructors<A>());
testRuntimeSpan<int>();
testRuntimeSpan<long>();
testRuntimeSpan<double>();
testRuntimeSpan<std::string>();
testRuntimeSpan<A>();
assert(testConstructors<int*>());
assert(testConstructors<int* const>());
assert(testConstructors<const int*>());
assert(testConstructors<const int* const>());
checkCV();
return 0;
return 0;
}

2
libcxx/www/cxx2a_status.html
View File

@ -490,7 +490,7 @@
<tr><td><a href="https://wg21.link/LWG3251">3251</a></td><td>Are <tt>std::format</tt> alignment specifiers applied to string arguments?</td><td>Prague</td><td></td></tr>
<tr><td><a href="https://wg21.link/LWG3252">3252</a></td><td>Parse locale's aware modifiers for commands are not consistent with POSIX spec</td><td>Prague</td><td></td></tr>
<tr><td><a href="https://wg21.link/LWG3254">3254</a></td><td>Strike <tt>stop_token</tt>'s <tt>operator!=</tt></td><td>Prague</td><td></td></tr>
<tr><td><a href="https://wg21.link/LWG3255">3255</a></td><td><tt>span</tt>'s <tt>array</tt> constructor is too strict</td><td>Prague</td><td></td></tr>
<tr><td><a href="https://wg21.link/LWG3255">3255</a></td><td><tt>span</tt>'s <tt>array</tt> constructor is too strict</td><td>Prague</td><td>Complete</td></tr>
<tr><td><a href="https://wg21.link/LWG3260">3260</a></td><td><tt>year_month*</tt> arithmetic rejects durations convertible to years</td><td>Prague</td><td></td></tr>
<tr><td><a href="https://wg21.link/LWG3262">3262</a></td><td>Formatting of negative durations is not specified</td><td>Prague</td><td></td></tr>
<tr><td><a href="https://wg21.link/LWG3264">3264</a></td><td><tt>sized_range</tt> and <tt>ranges::size</tt> redundantly use <tt>disable_sized_range</tt></td><td>Prague</td><td></td></tr>