[#mp_units-operator_3way-015]
= xref:mp_units.adoc[mp_units]::operator<=>
:relfileprefix: ../
:mrdocs:

Three‐way comparison operator

== Synopsis

Declared in `<mp‐units/framework/quantity.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    auto R1,
    typename Rep1>
requires std::three_way_comparable<Rep1> && requires { representation_values<Rep1>::zero(); }
[[nodiscard]]
constexpr
auto
operator<=>(
    xref:mp_units/quantity-01.adoc[quantity<R1, Rep1>] const& lhs,
    /* implementation-defined */ rhs);
----

[NOTE]
====
This function is a https://en.cppreference.com/w/cpp/language/friend[hidden friend] of xref:mp_units/quantity-01.adoc[quantity], declared inside an implementation-defined base class: it can be found only through argument-dependent lookup.
====

== Return Value

The relative order of the objects

[NOTE]
====
The return value https://en.cppreference.com/cpp/language/attributes/nodiscard[should not be discarded^].
====
== Parameters

[cols="1,4"]
|===
| Name| Description
| *lhs*
| The left operand
| *rhs*
| The right operand
|===


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