===={} ou std::nullopt====

C'est la même chose.

<code cpp>
#include <cassert>
#include <optional>

struct Version {
  Version() {}
  uint32_t major = 0;
  uint32_t minor = 0;
  uint32_t patch = 0;
};

int main() {
  std::optional<int> o1 = {};
  std::optional<int> o2 = 1;
  std::optional<Version> o3 = {};
  std::optional<Version> o4 = {{}};

  assert(!o1);
  assert(o2);
  assert(!o3);
  assert(o4);
}
</code>

[[https://stackoverflow.com/questions/57964217/stdoptional-construct-empty-with-or-stdnullopt|std::optional - construct empty with {} or std::nullopt?]] {{ :lang:cpp:optional:c_-_std_optional_-_construct_empty_with_or_std_nullopt_-_stack_overflow_01_02_2023_11_59_46_.html |Archive du 16/09/2019 le 01/02/2023}}

====std::make_optional====
''std::make_optional'' force la création d'un optional alors que std::optional peut copier un optional.

<code cpp>
#include <optional>
#include <type_traits>

int main()
{
    auto inner=std::make_optional(325);
    auto opt2=std::make_optional(inner); // makes std::optional<std::optional<int>>
    auto opt3=std::optional(inner);      // just a copy of inner
    static_assert(std::is_same_v<decltype(opt2), std::optional<std::optional<int>>>);
    static_assert(std::is_same_v<decltype(opt3), std::optional<int>>);
}
</code>

[[https://stackoverflow.com/questions/62734897/what-is-the-point-of-stdmake-optional|What is the point of `std::make_optional`]] {{ :lang:cpp:optional:c_-_what_is_the_point_of_std_make_optional_-_stack_overflow_14_03_2023_12_26_26_.html |Archive du 04/07/2020 le 14/03/2023}}

====Spécificités====
===Opérateur ternaire===

Il faut spécifier explicitement l'optional.

<code cpp>
std::optional<int> t;
t = true ? 1 : std::optional<int>{std::nullopt};
</code>