From 0c1128947b557c483c2268ec0418fe9dac93b414 Mon Sep 17 00:00:00 2001
From: terik23 <neargye@gmail.com>
Date: Thu, 11 Apr 2019 05:25:40 +0500
Subject: [PATCH] add integer_cast

---
 example/example.cpp    | 12 ++++++++++++
 include/magic_enum.hpp | 25 +++++++++++++++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/example/example.cpp b/example/example.cpp
index 86dde9e..5a84899 100644
--- a/example/example.cpp
+++ b/example/example.cpp
@@ -55,6 +55,18 @@ int main() {
     std::cout << "GREEN = " << c3.value() << std::endl; // GREEN = 10
   }
 
+  // Enum value to integer value.
+  auto color_underlying = magic_enum::integer_cast(Color::RED);
+  if (color_underlying.has_value() && color_underlying.value() == static_cast<std::underlying_type_t<Color>>(Color::RED)) {
+    std::cout << "RED = " << color_underlying.value() << std::endl; // RED = -10
+  }
+
+  // Enum value to specific type integer value.
+  auto color_int = magic_enum::integer_cast<int>(Color::RED);
+  if (color_int.has_value() && color_int.value() == static_cast<int>(Color::RED)) {
+    std::cout << "RED = " << color_int.value() << std::endl; // RED = -10
+  }
+
   using namespace magic_enum::ops; // out-of-the-box stream operator for enums.
   // ostream operator for enum.
   std::cout << "Color: " << c1 << " " << c2 << " " << c3 << std::endl; // Color: RED BLUE GREEN
diff --git a/include/magic_enum.hpp b/include/magic_enum.hpp
index 12daaf2..226b1fa 100644
--- a/include/magic_enum.hpp
+++ b/include/magic_enum.hpp
@@ -242,6 +242,31 @@ template <typename E, typename = detail::enable_if_enum_t<E>>
   }
 }
 
+// Obtains integer value from enum value.
+template <typename E, typename D = std::decay_t<E>, typename = detail::enable_if_enum_t<D>>
+[[nodiscard]] constexpr std::optional<std::underlying_type_t<D>> integer_cast(E value) noexcept {
+  static_assert(std::is_enum_v<D>, "magic_enum::integer_cast requires enum type.");
+
+  if (detail::name_impl<D>(static_cast<int>(value)).empty()) {
+    return std::nullopt; // Invalid value or out of range.
+  } else {
+    return static_cast<std::underlying_type_t<D>>(value);
+  }
+}
+
+// Obtains specific type integer value from enum value.
+template <typename I, typename E, typename D = std::decay_t<E>, typename = std::enable_if_t<std::is_enum_v<D> && std::is_arithmetic_v<I>>>
+[[nodiscard]] constexpr std::optional<I> integer_cast(E value) noexcept {
+  static_assert(std::is_enum_v<D>, "magic_enum::integer_cast requires enum type.");
+  static_assert(std::is_arithmetic_v<I>, "magic_enum::integer_cast requires integer type.");
+
+  if (detail::name_impl<D>(static_cast<int>(value)).empty() || static_cast<I>(value) != static_cast<std::underlying_type_t<D>>(value)) {
+    return std::nullopt; // Invalid value or out of range.
+  } else {
+    return static_cast<I>(value);
+  }
+}
+
 // Returns enum value at specified index.
 // No bounds checking is performed: the behavior is undefined if index >= number of enum values.
 template<typename E, typename = detail::enable_if_enum_t<E>>