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-rw-r--r--src/span.h19
1 files changed, 19 insertions, 0 deletions
diff --git a/src/span.h b/src/span.h
index 9379b15c81..a7e0020b9a 100644
--- a/src/span.h
+++ b/src/span.h
@@ -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().