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Support conversion between Spans of compatible types

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This commit is contained in:
Pieter Wuille 2020-03-29 16:08:45 -07:00
parent 7cbfebbf3d
commit 0fbde488b2
1 changed files with 19 additions and 0 deletions
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19
src/span.h
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@ -25,6 +25,23 @@ public:
constexpr Span(C* data, std::ptrdiff_t size) noexcept : m_data(data), m_size(size) {}
constexpr Span(C* data, C* end) noexcept : m_data(data), m_size(end - data) {}
/** Implicit conversion of spans between compatible types.
*
* Specifically, if a pointer to an array of type O can be implicitly converted to a pointer to an array of type
* C, then permit implicit conversion of Span<O> to Span<C>. This matches the behavior of the corresponding
* C++20 std::span constructor.
*
* For example this means that a Span<T> can be converted into a Span<const T>.
*/
template <typename O, typename std::enable_if<std::is_convertible<O (*)[], C (*)[]>::value, int>::type = 0>
constexpr Span(const Span<O>& other) noexcept : m_data(other.m_data), m_size(other.m_size) {}
/** Default copy constructor. */
constexpr Span(const Span&) noexcept = default;
/** Default assignment operator. */
Span& operator=(const Span& other) noexcept = default;
constexpr C* data() const noexcept { return m_data; }
constexpr C* begin() const noexcept { return m_data; }
constexpr C* end() const noexcept { return m_data + m_size; }
@ -44,6 +61,8 @@ public:
friend constexpr bool operator<=(const Span& a, const Span& b) noexcept { return !(b < a); }
friend constexpr bool operator>(const Span& a, const Span& b) noexcept { return (b < a); }
friend constexpr bool operator>=(const Span& a, const Span& b) noexcept { return !(a < b); }
template <typename O> friend class Span;
};
/** Create a span to a container exposing data() and size().