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span: (almost) match std::span's constructor behavior

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c++20's draft of std::span no longer includes move constructors.
This commit is contained in:
Cory Fields 2020-06-26 13:21:13 -04:00
parent f32f7e907a
commit 62733fee87
1 changed files with 21 additions and 2 deletions
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23
src/span.h
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@ -28,6 +28,14 @@ class Span
C* m_data; C* m_data;
std::size_t m_size; std::size_t m_size;
template <class T>
struct is_Span_int : public std::false_type {};
template <class T>
struct is_Span_int<Span<T>> : public std::true_type {};
template <class T>
struct is_Span : public is_Span_int<typename std::remove_cv<T>::type>{};
public: public:
constexpr Span() noexcept : m_data(nullptr), m_size(0) {} constexpr Span() noexcept : m_data(nullptr), m_size(0) {}
@ -78,8 +86,19 @@ public:
* To prevent surprises, only Spans for constant value types are supported when passing in temporaries. * To prevent surprises, only Spans for constant value types are supported when passing in temporaries.
* Note that this restriction does not exist when converting arrays or other Spans (see above). * Note that this restriction does not exist when converting arrays or other Spans (see above).
*/ */
template <typename V, typename std::enable_if<(std::is_const<C>::value || std::is_lvalue_reference<V>::value) && std::is_convertible<typename std::remove_pointer<decltype(std::declval<V&>().data())>::type (*)[], C (*)[]>::value && std::is_convertible<decltype(std::declval<V&>().size()), std::size_t>::value, int>::type = 0> template <typename V>
constexpr Span(V&& v) noexcept : m_data(v.data()), m_size(v.size()) {} constexpr Span(V& other,
typename std::enable_if<!is_Span<V>::value &&
std::is_convertible<typename std::remove_pointer<decltype(std::declval<V&>().data())>::type (*)[], C (*)[]>::value &&
std::is_convertible<decltype(std::declval<V&>().size()), std::size_t>::value, std::nullptr_t>::type = nullptr)
: m_data(other.data()), m_size(other.size()){}
template <typename V>
constexpr Span(const V& other,
typename std::enable_if<!is_Span<V>::value &&
std::is_convertible<typename std::remove_pointer<decltype(std::declval<const V&>().data())>::type (*)[], C (*)[]>::value &&
std::is_convertible<decltype(std::declval<const V&>().size()), std::size_t>::value, std::nullptr_t>::type = nullptr)
: m_data(other.data()), m_size(other.size()){}
constexpr C* data() const noexcept { return m_data; } constexpr C* data() const noexcept { return m_data; }
constexpr C* begin() const noexcept { return m_data; } constexpr C* begin() const noexcept { return m_data; }