1 files changed, 49 insertions, 0 deletions
diff --git a/boost/histogram/detail/try_cast.hpp b/boost/histogram/detail/try_cast.hpp
new file mode 100644
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+++ b/boost/histogram/detail/try_cast.hpp
@@ -0,0 +1,49 @@
+// Copyright 2019 Hans Dembinski
+//
+// Distributed under the Boost Software License, Version 1.0.
+// (See accompanying file LICENSE_1_0.txt
+// or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_HISTOGRAM_DETAIL_TRY_CAST_HPP
+#define BOOST_HISTOGRAM_DETAIL_TRY_CAST_HPP
+
+#include <boost/config.hpp>
+#include <boost/core/demangle.hpp>
+#include <boost/histogram/detail/cat.hpp>
+#include <boost/histogram/detail/type_name.hpp>
+#include <boost/mp11/integral.hpp>
+#include <boost/throw_exception.hpp>
+#include <stdexcept>
+#include <type_traits>
+
+namespace boost {
+namespace histogram {
+namespace detail {
+template <class T, class E, class U>
+BOOST_NORETURN T try_cast_impl(mp11::mp_int<0>, U&&) {
+  BOOST_THROW_EXCEPTION(E(cat("cannot cast ", type_name<T>(), " to ", type_name<U>())));
+}
+
+template <class T, class E, class U>
+T try_cast_impl(mp11::mp_int<1>, U&& u) noexcept {
+  return static_cast<T>(u);
+}
+
+template <class T, class E, class U>
+decltype(auto) try_cast_impl(mp11::mp_int<2>, U&& u) noexcept {
+  return std::forward<U>(u);
+}
+
+// cast fails at runtime with exception E instead of compile-time, T must be a value
+template <class T, class E, class U>
+decltype(auto) try_cast(U&& u) noexcept(std::is_convertible<U, T>::value) {
+  return try_cast_impl<T, E>(mp11::mp_int<(std::is_convertible<U, T>::value +
+                                           std::is_same<T, std::decay_t<U>>::value)>{},
+                             std::forward<U>(u));
+}
+
+} // namespace detail
+} // namespace histogram
+} // namespace boost
+
+#endif