Merge #18591: Add C++17 build to Travis

c31cbe7cfe Add C++17 test to Travis (Pieter Wuille)
7829685e27 Add configure option for c++17 (Pieter Wuille)
0fbde488b2 Support conversion between Spans of compatible types (Pieter Wuille)
7cbfebbf3d Update ax_cxx_compile_stdcxx.m4 (Pieter Wuille)

Pull request description:

  This adds a `--enable-c++17` option to the configure script, fixes the only C++17 incompatibility (with a commit taken from #18468), and adds a Travis test for it.

  This is all off by default, and release builds remain C++11.

  It implements the first step of the plan in https://github.com/bitcoin/bitcoin/issues/16684.

ACKs for top commit:
  elichai:
    tACK c31cbe7cfe
  practicalswift:
    Tested ACK c31cbe7cfe
  hebasto:
    ACK c31cbe7cfe, tested on Linux Mint 19.3 both C++11 and C++17 modes. Compiled and passed tests locally.

Tree-SHA512: a4b00776dbceef9c12abbb404c6bcd48f7916ce24c8c7a14116355f64e817578b7fcddbedd5ce435322319d1e4de43429b68553f4d96d970c308fe3e3e59b9d1
This commit is contained in:
Wladimir J. van der Laan
2020-04-30 11:16:39 +02:00
5 changed files with 470 additions and 38 deletions

View File

@ -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().