[#beman-optional-operator_3way-04]
= xref:beman.adoc[beman]::xref:beman/optional.adoc[optional]::operator<=>
:relfileprefix: ../../
:mrdocs:

Three‐way comparison operators

== Synopses

Declared in `<beman/optional/optional.hpp>`

Compares two `nullopt_t` objects.


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
constexpr
std::strong_ordering
xref:beman/optional/operator_3way-0a.adoc[operator<=>](
    xref:beman/optional/nullopt_t.adoc[nullopt_t] lhs,
    xref:beman/optional/nullopt_t.adoc[nullopt_t] rhs) noexcept;
----

[.small]#xref:beman/optional/operator_3way-0a.adoc[_» more..._]#

Three‐way comparison of two optionals.


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    typename T,
    std::three_way_comparable_with<T> U>
constexpr
std::compare_three_way_result_t<T, U>
xref:beman/optional/operator_3way-09.adoc[operator<=>](
    xref:beman/optional/optional-03.adoc[optional<T>] const& lhs,
    xref:beman/optional/optional-03.adoc[optional<U>] const& rhs);
----

[.small]#xref:beman/optional/operator_3way-09.adoc[_» more..._]#

Three‐way comparison of an optional against `nullopt`.


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<class T>
constexpr
std::strong_ordering
xref:beman/optional/operator_3way-05.adoc[operator<=>](
    xref:beman/optional/optional-03.adoc[optional<T>] const& lhs,
    xref:beman/optional/nullopt_t.adoc[nullopt_t] rhs) noexcept;
----

[.small]#xref:beman/optional/operator_3way-05.adoc[_» more..._]#

Three‐way comparison of an optional against a value.


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    typename T,
    typename U>
requires (!is_derived_from_optional<U>) && std::three_way_comparable_with<T, U>
constexpr
std::compare_three_way_result_t<T, U>
xref:beman/optional/operator_3way-08.adoc[operator<=>](
    xref:beman/optional/optional-03.adoc[optional<T>] const& x,
    U const& v);
----

[.small]#xref:beman/optional/operator_3way-08.adoc[_» more..._]#

== Return Value

* Always `std::strong_ordering::equivalent`, since all `nullopt_t` objects compare equal.
* The comparison category; a disengaged optional orders before any engaged one.
* `equivalent` if `lhs` is disengaged, otherwise `greater`.
* The comparison category; a disengaged optional orders before `v.`

== Parameters

[cols="1,4"]
|===
| Name| Description
| *lhs*
| The left‐hand `nullopt_t` object.
| *rhs*
| The right‐hand `nullopt_t` object.
| *x*
| The optional operand.
| *v*
| The value operand.
|===


[.small]#Created with https://www.mrdocs.com[MrDocs]#