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4497. std::nullopt_t should be comparable

Section: 22.5.5 [optional.nullopt] Status: WP Submitter: Barry Revzin Opened: 2025-12-21 Last modified: 2026-03-31

Priority: 2

View all other issues in [optional.nullopt].

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Discussion:

std::nullopt_t currently has no comparison operators. This prevents perfectly reasonable code from working, like ranges::find(v, nullopt) where v is a vector<optional<T>>, for no good reason.

Additionally, optional<T> has the full set of comparisons. But optional<T> is conceptually a variant<nullopt_t, T>, which wouldn't be comparable... because of nullopt_t. Other empty types like tuple<> and monostate are also comparable.

Proposed resolution: Add a defaulted member operator<=> to nullopt_t.

[2026-02-18; Reflector poll.]

Set priority to 2 after reflector poll.

Discussion whether this needs LEWG approval. Paper P2405, for which the nullopt part received LEWG support, is relevant here.

[2026-03-26; Tim provides wording]

[Croydon 2026-03-27; Status changed: New → Immediate.]

[Croydon 2026-03-28; Status changed: Immediate → WP.]

Proposed resolution:

This wording is relative to N5032.

1. Edit 22.5.5 [optional.nullopt], as indicated:

   struct nullopt_t{see below};
   inline constexpr nullopt_t nullopt(unspecified);
   

   -1- […]

   -2- Type nullopt_t shalldoes not have a default constructor or an initializer-list constructor, and shall not beis not an aggregate. nullopt_t models copyable and three_way_comparable<strong_ordering>.