add enum_min and enum_max

doc/reference.md

@@ -4,6 +4,7 @@
 * [`enum_value` returns enum value at specified index.](#enum_value)
 * [`enum_values` returns enum value sequence.](#enum_values)
 * [`enum_count` returns number of enum values.](#enum_count)
+* [`enum_min` and `enum_max` return the minimum and maximum enum values.](#enum_min-and-enum_max)
 * [`enum_integer` returns integer value from enum value.](#enum_integer)
 * [`enum_name` returns name from enum value.](#enum_name)
 * [`enum_names` returns string enum name sequence.](#enum_names)
@@ -185,6 +186,31 @@ constexpr size_t enum_count() noexcept;
   // color_count -> 3
   ```
 
+## `enum_min` and `enum_max`
+
+```cpp
+template <typename E>
+constexpr E enum_min() noexcept;
+
+template <typename E>
+constexpr E enum_max() noexcept;
+```
+
+* Defined in header `<magic_enum/magic_enum.hpp>`
+
+* Return the minimum and maximum reflected enum values, respectively, sorted by enum value.
+
+* The enum subtype can be provided explicitly, for example `magic_enum::enum_max<MyEnum, magic_enum::as_flags<>>()`.
+
+* Examples
+
+  ```cpp
+  constexpr auto color_min = magic_enum::enum_min<Color>();
+  constexpr auto color_max = magic_enum::enum_max<Color>();
+  // color_min -> Color::RED
+  // color_max -> Color::GREEN
+  ```
+
 ## `enum_integer`
 
 ```cpp

include/magic_enum/magic_enum.hpp

@@ -1236,6 +1236,24 @@ template <typename E, detail::enum_subtype S = detail::subtype_v<E>>
   return detail::count_v<std::decay_t<E>, S>;
 }
 
+// Returns minimum enum value.
+template <typename E, detail::enum_subtype S = detail::subtype_v<E>>
+[[nodiscard]] constexpr auto enum_min() noexcept -> detail::enable_if_t<E, std::decay_t<E>> {
+  using D = std::decay_t<E>;
+  static_assert(detail::count_v<D, S> > 0, "magic_enum::enum_min requires at least one reflected enum value.");
+
+  return detail::values_v<D, S>.front();
+}
+
+// Returns maximum enum value.
+template <typename E, detail::enum_subtype S = detail::subtype_v<E>>
+[[nodiscard]] constexpr auto enum_max() noexcept -> detail::enable_if_t<E, std::decay_t<E>> {
+  using D = std::decay_t<E>;
+  static_assert(detail::count_v<D, S> > 0, "magic_enum::enum_max requires at least one reflected enum value.");
+
+  return detail::values_v<D, S>.back();
+}
+
 // Returns enum value at specified index.
 // No bounds checking is performed: the behavior is undefined if index >= number of enum values.
 template <typename E, detail::enum_subtype S = detail::subtype_v<E>>

test/test.cpp

@@ -523,6 +523,20 @@ TEST_CASE("enum_count") {
   REQUIRE(s6 == 2);
 }
 
+TEST_CASE("enum_min_max") {
+  constexpr auto color_min = enum_min<Color&>();
+  constexpr auto color_max = enum_max<const Color>();
+  REQUIRE(color_min == Color::RED);
+  REQUIRE(color_max == Color::BLUE);
+  static_assert(enum_underlying(color_min) == -12);
+  static_assert(enum_underlying(color_max) == 15);
+
+  REQUIRE(enum_min<Directions>() == Directions::Left);
+  REQUIRE(enum_max<Directions>() == Directions::Right);
+  REQUIRE(enum_min<number>() == number::one);
+  REQUIRE(enum_max<number>() == number::three);
+}
+
 enum lt1 { s1, loooooooooooooooooooong1 };
 enum lt2 : unsigned { s2, loooooooooooooooooooong2 };
 enum class lt3 { s3, loooooooooooooooooooong3 };

test/test_flags.cpp

@@ -476,6 +476,25 @@ TEST_CASE("enum_count") {
   REQUIRE(s4 == 4);
 }
 
+TEST_CASE("enum_min_max") {
+  constexpr auto color_min = enum_min<Color>();
+  constexpr auto color_max = enum_max<Color, as_flags<>>();
+  REQUIRE(color_min == Color::RED);
+  REQUIRE(color_max == Color::BLUE);
+  static_assert(color_min == Color::RED);
+  static_assert(color_max == Color::BLUE);
+
+  constexpr auto directions_min = enum_min<Directions>();
+  constexpr auto directions_max = enum_max<Directions>();
+  REQUIRE(directions_min == Directions::Left);
+  REQUIRE(directions_max == Directions::Right);
+  static_assert(directions_min == Directions::Left);
+  static_assert(directions_max == Directions::Right);
+
+  REQUIRE(enum_min<number>() == number::one);
+  REQUIRE(enum_max<number>() == number::four);
+}
+
 TEST_CASE("enum_name") {
   SUBCASE("automatic storage") {
     constexpr Color cr = Color::RED;