Tightened SFINAE for span<U> to span<T> conversions.
diff --git a/include/span.h b/include/span.h
index 7152c2d..676fdf2 100644
--- a/include/span.h
+++ b/include/span.h
@@ -77,6 +77,11 @@
class span;
+// [views.constants], constants
+constexpr const std::ptrdiff_t dynamic_extent = -1;
+
+
+// implementation details
namespace details
{
template <class T>
@@ -96,45 +101,55 @@
template <class From, class To>
struct is_allowed_pointer_conversion
- : std::integral_constant<bool,
- std::is_pointer<From>::value &&
- std::is_pointer<To>::value &&
- std::is_convertible<From, To>::value
+ : std::bool_constant<
+ std::is_pointer<From>::value &&
+ std::is_pointer<To>::value &&
+ std::is_convertible<From, To>::value
>
{
};
template <class From, class To>
struct is_allowed_integral_conversion
- : std::integral_constant<bool,
- std::is_integral<From>::value &&
- std::is_integral<To>::value &&
- sizeof(From) == sizeof(To) &&
- alignof(From) == alignof(To) &&
- std::is_convertible<From, To>::value
+ : std::bool_constant<
+ std::is_integral<From>::value &&
+ std::is_integral<To>::value &&
+ sizeof(From) == sizeof(To) &&
+ alignof(From) == alignof(To) &&
+ std::is_convertible<From, To>::value
+ >
+{
+};
+
+template <std::ptrdiff_t From, std::ptrdiff_t To>
+struct is_allowed_extent_conversion
+ : std::bool_constant<
+ From == To ||
+ From == gsl::dynamic_extent ||
+ To == gsl::dynamic_extent
>
{
};
template <class From, class To>
struct is_allowed_element_type_conversion
- : std::integral_constant<bool,
- std::is_same<From, std::remove_cv_t<To>>::value ||
- is_allowed_pointer_conversion<From, To>::value ||
- is_allowed_integral_conversion<From, To>::value
+ : std::bool_constant<
+ std::is_same<From, std::remove_cv_t<To>>::value ||
+ is_allowed_pointer_conversion<From, To>::value ||
+ is_allowed_integral_conversion<From, To>::value
>
{
};
template <class From>
struct is_allowed_element_type_conversion<From, byte>
- : std::integral_constant<bool, !std::is_const<From>::value>
+ : std::bool_constant<!std::is_const<From>::value>
{
};
template <class From>
struct is_allowed_element_type_conversion<From, const byte>
- : std::integral_constant<bool, true>
+ : std::true_type
{
};
@@ -191,7 +206,7 @@
auto ret{*this};
return ret += n;
}
-
+
span_iterator& operator+=(difference_type n) noexcept
{
index_ += n;
@@ -217,10 +232,14 @@
}
reference operator[](difference_type n) const noexcept
- { return *(*this + n); }
+ {
+ return *(*this + n);
+ }
bool operator==(const span_iterator& rhs) const noexcept
- { return span_ == rhs.span_ && index_ == rhs.index_; }
+ {
+ return span_ == rhs.span_ && index_ == rhs.index_;
+ }
bool operator!=(const span_iterator& rhs) const noexcept { return !(*this == rhs); }
@@ -231,9 +250,9 @@
}
bool operator<=(const span_iterator& rhs) const noexcept { return !(rhs < *this); }
-
+
bool operator>(const span_iterator& rhs) const noexcept { return rhs < *this; }
-
+
bool operator>=(const span_iterator& rhs) const noexcept { return !(rhs > *this); }
void swap(span_iterator& rhs) noexcept
@@ -250,21 +269,20 @@
template <typename Span>
span_iterator<Span> operator+(typename span_iterator<Span>::difference_type n,
const span_iterator<Span>& rhs) noexcept
-{ return rhs + n; }
+{
+ return rhs + n;
+}
template <typename Span>
span_iterator<Span> operator-(typename span_iterator<Span>::difference_type n,
const span_iterator<Span>& rhs) noexcept
-{ return rhs - n; }
-
+{
+ return rhs - n;
+}
} // namespace details
-// [views.constants], constants
-constexpr const std::ptrdiff_t dynamic_extent = -1;
-
-
// [span], class template span
template <class ElementType, std::ptrdiff_t Extent>
class span {
@@ -330,21 +348,23 @@
constexpr span(span&& other) noexcept = default;
template <class OtherElementType, std::ptrdiff_t OtherExtent,
- class = std::enable_if_t<!std::is_same<element_type, OtherElementType>::value &&
+ class = std::enable_if_t<
+ details::is_allowed_extent_conversion<OtherExtent, Extent>::value &&
details::is_allowed_element_type_conversion<OtherElementType, element_type>::value
>
>
constexpr span(const span<OtherElementType, OtherExtent>& other)
- : storage_(reinterpret_cast<pointer>(other.data()), other.length())
+ : storage_(reinterpret_cast<pointer>(other.data()), extent_type<OtherExtent>(other.size()))
{}
template <class OtherElementType, std::ptrdiff_t OtherExtent,
- class = std::enable_if_t<!std::is_same<element_type, OtherElementType>::value &&
+ class = std::enable_if_t<
+ details::is_allowed_extent_conversion<OtherExtent, Extent>::value &&
details::is_allowed_element_type_conversion<OtherElementType, element_type>::value
>
>
constexpr span(span<OtherElementType, OtherExtent>&& other)
- : storage_(reinterpret_cast<pointer>(other.data()), other.length())
+ : storage_(reinterpret_cast<pointer>(other.data()), extent_type<OtherExtent>(other.size()))
{}
~span() noexcept = default;
@@ -418,6 +438,8 @@
reverse_iterator rend() const noexcept { return {this, 0}; }
private:
+ constexpr static const bool is_span_type = true;
+
template <index_type Extent>
class extent_type;
@@ -430,10 +452,11 @@
constexpr extent_type() noexcept {}
template <index_type Other>
- constexpr extent_type(extent_type<Other>) noexcept
+ constexpr extent_type(extent_type<Other> ext) noexcept
{
- static_assert(Other == Extent,
+ static_assert(Other == Extent || Other == dynamic_extent,
"Mismatch between fixed-size extent and size of initializing data.");
+ Expects(ext.size() == Extent);
}
constexpr extent_type(index_type size)