ceph/src/boost/boost/histogram/detail/try_cast.hpp

   1 // Copyright 2019 Hans Dembinski
   2 //
   3 // Distributed under the Boost Software License, Version 1.0.
   4 // (See accompanying file LICENSE_1_0.txt
   5 // or copy at http://www.boost.org/LICENSE_1_0.txt)
   6
   7 #ifndef BOOST_HISTOGRAM_DETAIL_TRY_CAST_HPP
   8 #define BOOST_HISTOGRAM_DETAIL_TRY_CAST_HPP
   9
  10 #include <boost/config.hpp> // BOOST_NORETURN
  11 #include <boost/throw_exception.hpp>
  12 #include <type_traits>
  13
  14 namespace boost {
  15 namespace histogram {
  16 namespace detail {
  17
  18 template <class T, class U>
  19 constexpr T* ptr_cast(U*) noexcept {
  20   return nullptr;
  21 }
  22
  23 template <class T>
  24 constexpr T* ptr_cast(T* p) noexcept {
  25   return p;
  26 }
  27
  28 template <class T>
  29 constexpr const T* ptr_cast(const T* p) noexcept {
  30   return p;
  31 }
  32
  33 template <class T, class E, class U>
  34 BOOST_NORETURN T try_cast_impl(std::false_type, std::false_type, U&&) {
  35   BOOST_THROW_EXCEPTION(E("type cast error"));
  36 }
  37
  38 // converting cast
  39 template <class T, class E, class U>
  40 T try_cast_impl(std::false_type, std::true_type, U&& u) noexcept {
  41   return static_cast<T>(u); // cast to avoid warnings
  42 }
  43
  44 // pass-through cast
  45 template <class T, class E>
  46 T&& try_cast_impl(std::true_type, std::true_type, T&& t) noexcept {
  47   return std::forward<T>(t);
  48 }
  49
  50 // cast fails at runtime with exception E instead of compile-time, T must be a value
  51 template <class T, class E, class U>
  52 T try_cast(U&& u) noexcept(std::is_convertible<U, T>::value) {
  53   return try_cast_impl<T, E>(std::is_same<U, T>{}, std::is_convertible<U, T>{},
  54                              std::forward<U>(u));
  55 }
  56
  57 } // namespace detail
  58 } // namespace histogram
  59 } // namespace boost
  60
  61 #endif