jdoerrie created this revision.
jdoerrie added reviewers: mclow.lists, ldionne.
Herald added a reviewer: EricWF.
Herald added subscribers: libcxx-commits, dexonsmith, christof.
[libc++] Disallow dynamic -> static span conversions
This change disallows dynamic to static span conversions. This complies
with the standard, which lists the following constaint in
views.span#span.cons-20.1 [1]:
Extent == dynamic_extent || Extent == OtherExtent
Thus this should fail if Extent != dynamic_extent && Extent !=
OtherExtent, which is the case when trying to construct a static span
from a dynamic span.
[1] https://eel.is/c++draft/views.span#span.cons-20.1
Repository:
rCXX libc++
https://reviews.llvm.org/D69520
Files:
libcxx/include/span
libcxx/test/std/containers/views/span.cons/span.fail.cpp
libcxx/test/std/containers/views/span.cons/span.pass.cpp
Index: libcxx/test/std/containers/views/span.cons/span.pass.cpp
===================================================================
--- libcxx/test/std/containers/views/span.cons/span.pass.cpp
+++ libcxx/test/std/containers/views/span.cons/span.pass.cpp
@@ -62,48 +62,41 @@
std::span<const volatile int> s4{ vsp0}; // a span<const volatile int> pointing at volatile int.
assert(s1.size() + s2.size() + s3.size() + s4.size() == 0);
}
-
-// dynamic -> static
- {
- std::span<const int, 0> s1{ sp}; // a span<const int> pointing at int.
- std::span< volatile int, 0> s2{ sp}; // a span< volatile int> pointing at int.
- std::span<const volatile int, 0> s3{ sp}; // a span<const volatile int> pointing at int.
- std::span<const volatile int, 0> s4{ vsp}; // a span<const volatile int> pointing at volatile int.
- assert(s1.size() + s2.size() + s3.size() + s4.size() == 0);
- }
}
template <typename T>
constexpr bool testConstexprSpan()
{
- std::span<T> s0{};
- std::span<T, 0> s1(s0); // dynamic -> static
- std::span<T> s2(s1); // static -> dynamic
- ASSERT_NOEXCEPT(std::span<T> {s0});
- ASSERT_NOEXCEPT(std::span<T, 0>{s1});
- ASSERT_NOEXCEPT(std::span<T> {s1});
- ASSERT_NOEXCEPT(std::span<T, 0>{s0});
-
- return
- s1.data() == nullptr && s1.size() == 0
- && s2.data() == nullptr && s2.size() == 0;
+ std::span<T> s0d{};
+ std::span<T, 0> s0s{};
+ std::span<T> s1(s0d); // dynamic -> dynamic
+ std::span<T, 0> s2(s0s); // static -> static
+ std::span<T> s3(s2); // static -> dynamic
+ ASSERT_NOEXCEPT(std::span<T>{s0d});
+ ASSERT_NOEXCEPT(std::span<T, 0>{s0s});
+ ASSERT_NOEXCEPT(std::span<T>{s0s});
+
+ return s1.data() == nullptr && s1.size() == 0 && s2.data() == nullptr &&
+ s2.size() == 0 && s3.data() == nullptr && s3.size() == 0;
}
template <typename T>
void testRuntimeSpan()
{
- std::span<T> s0{};
- std::span<T, 0> s1(s0); // dynamic -> static
- std::span<T> s2(s1); // static -> dynamic
- ASSERT_NOEXCEPT(std::span<T> {s0});
- ASSERT_NOEXCEPT(std::span<T, 0>{s1});
- ASSERT_NOEXCEPT(std::span<T> {s1});
- ASSERT_NOEXCEPT(std::span<T, 0>{s0});
-
- assert(s1.data() == nullptr && s1.size() == 0);
- assert(s2.data() == nullptr && s2.size() == 0);
+ std::span<T> s0d{};
+ std::span<T, 0> s0s{};
+ std::span<T> s1(s0d); // dynamic -> dynamic
+ std::span<T, 0> s2(s0s); // static -> static
+ std::span<T> s3(s2); // static -> dynamic
+ ASSERT_NOEXCEPT(std::span<T>{s0d});
+ ASSERT_NOEXCEPT(std::span<T, 0>{s0s});
+ ASSERT_NOEXCEPT(std::span<T>{s0s});
+
+ assert(s1.data() == nullptr && s1.size() == 0);
+ assert(s2.data() == nullptr && s2.size() == 0);
+ assert(s3.data() == nullptr && s3.size() == 0);
}
@@ -113,10 +106,12 @@
static_assert(std::is_convertible_v<Src(*)[], Dest(*)[]>, "Bad input types to 'testConversionSpan");
std::span<Src> s0d{};
std::span<Src> s0s{};
- std::span<Dest, 0> s1(s0d); // dynamic -> static
- std::span<Dest> s2(s0s); // static -> dynamic
- s1.data() == nullptr && s1.size() == 0
- && s2.data() == nullptr && s2.size() == 0;
+ std::span<Dest> s1(s0d); // dynamic -> dynamic
+ std::span<Dest, 0> s2(s0s); // static -> static
+ std::span<Dest> s3(s0d); // static -> dynamic
+ s1.data() == nullptr&& s1.size() == 0 &&
+ s2.data() == nullptr&& s2.size() == 0 &&
+ s3.data() == nullptr&& s3.size() == 0;
}
struct A{};
Index: libcxx/test/std/containers/views/span.cons/span.fail.cpp
===================================================================
--- libcxx/test/std/containers/views/span.cons/span.fail.cpp
+++ libcxx/test/std/containers/views/span.cons/span.fail.cpp
@@ -74,19 +74,6 @@
std::span< volatile int> s6{ csp0}; // expected-error {{no matching constructor for initialization of 'std::span<volatile int>'}}
std::span< volatile int> s7{cvsp0}; // expected-error {{no matching constructor for initialization of 'std::span<volatile int>'}}
}
-
-// Try to remove const and/or volatile (static -> static)
- {
- std::span< int, 0> s1{ csp}; // expected-error {{no matching constructor for initialization of 'std::span<int, 0>'}}
- std::span< int, 0> s2{ vsp}; // expected-error {{no matching constructor for initialization of 'std::span<int, 0>'}}
- std::span< int, 0> s3{cvsp}; // expected-error {{no matching constructor for initialization of 'std::span<int, 0>'}}
-
- std::span<const int, 0> s4{ vsp}; // expected-error {{no matching constructor for initialization of 'std::span<const int, 0>'}}
- std::span<const int, 0> s5{cvsp}; // expected-error {{no matching constructor for initialization of 'std::span<const int, 0>'}}
-
- std::span< volatile int, 0> s6{ csp}; // expected-error {{no matching constructor for initialization of 'std::span<volatile int, 0>'}}
- std::span< volatile int, 0> s7{cvsp}; // expected-error {{no matching constructor for initialization of 'std::span<volatile int, 0>'}}
- }
}
int main(int, char**)
Index: libcxx/include/span
===================================================================
--- libcxx/include/span
+++ libcxx/include/span
@@ -232,15 +232,6 @@
nullptr_t> = nullptr)
: __data{__other.data()} {}
- template <class _OtherElementType>
- _LIBCPP_INLINE_VISIBILITY
- constexpr span(const span<_OtherElementType, dynamic_extent>& __other,
- enable_if_t<
- is_convertible_v<_OtherElementType(*)[], element_type (*)[]>,
- nullptr_t> = nullptr) noexcept
- : __data{__other.data()} { _LIBCPP_ASSERT(_Extent == __other.size(), "size mismatch in span's constructor (other span)"); }
-
-
// ~span() noexcept = default;
template <size_t _Count>
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