Merge bitcoin#19387: span: update constructors to match c++20 draft s…

…pec and add lifetimebound attribute bitcoin@62733fe bitcoin@1d58cc7 bitcoin@e3e7446
dashpay · Apr 23, 2021 · 5667698 · 5667698
1 parent ec2eec0
commit 5667698
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Showing 2 changed files with 43 additions and 4 deletions.
diff --git a/src/attributes.h b/src/attributes.h
@@ -19,4 +19,14 @@
 #  endif
 #endif
 
+#if defined(__clang__)
+#  if __has_attribute(lifetimebound)
+#    define LIFETIMEBOUND [[clang::lifetimebound]]
+#  else
+#    define LIFETIMEBOUND
+#  endif
+#else
+#  define LIFETIMEBOUND
+#endif
+
 #endif // BITCOIN_ATTRIBUTES_H
diff --git a/src/span.h b/src/span.h
@@ -18,6 +18,16 @@
 #define ASSERT_IF_DEBUG(x)
 #endif
 
+#if defined(__clang__)
+#if __has_attribute(lifetimebound)
+#define SPAN_ATTR_LIFETIMEBOUND [[clang::lifetimebound]]
+#else
+#define SPAN_ATTR_LIFETIMEBOUND
+#endif
+#else
+#define SPAN_ATTR_LIFETIMEBOUND
+#endif
+
 /** A Span is an object that can refer to a contiguous sequence of objects.
  *
  * It implements a subset of C++20's std::span.
@@ -28,6 +38,14 @@ class Span
     C* m_data;
     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:
     constexpr Span() noexcept : m_data(nullptr), m_size(0) {}
 
@@ -78,8 +96,19 @@ class Span
      * 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).
      */
-    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>
-    constexpr Span(V&& v) noexcept : m_data(v.data()), m_size(v.size()) {}
+    template <typename V>
+    constexpr Span(V& other SPAN_ATTR_LIFETIMEBOUND,
+        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 SPAN_ATTR_LIFETIMEBOUND,
+        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* begin() const noexcept { return m_data; }
@@ -135,9 +164,9 @@ class Span
 /** MakeSpan for arrays: */
 template <typename A, int N> Span<A> constexpr MakeSpan(A (&a)[N]) { return Span<A>(a, N); }
 /** MakeSpan for temporaries / rvalue references, only supporting const output. */
-template <typename V> constexpr auto MakeSpan(V&& v) -> typename std::enable_if<!std::is_lvalue_reference<V>::value, Span<const typename std::remove_pointer<decltype(v.data())>::type>>::type { return std::forward<V>(v); }
+template <typename V> constexpr auto MakeSpan(V&& v SPAN_ATTR_LIFETIMEBOUND) -> typename std::enable_if<!std::is_lvalue_reference<V>::value, Span<const typename std::remove_pointer<decltype(v.data())>::type>>::type { return std::forward<V>(v); }
 /** MakeSpan for (lvalue) references, supporting mutable output. */
-template <typename V> constexpr auto MakeSpan(V& v) -> Span<typename std::remove_pointer<decltype(v.data())>::type> { return v; }
+template <typename V> constexpr auto MakeSpan(V& v SPAN_ATTR_LIFETIMEBOUND) -> Span<typename std::remove_pointer<decltype(v.data())>::type> { return v; }
 
 /** Pop the last element off a span, and return a reference to that element. */
 template <typename T>