[#mp_units-operator_minus-03a]
= xref:mp_units.adoc[mp_units]::operator‐
:relfileprefix: ../
:mrdocs:

Subtraction operator

== Synopsis

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

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    xref:mp_units/PointOrigin.adoc[PointOrigin] PO1,
    /* implementation-defined */ PO2>
requires (PointOriginFor<PO2, get_quantity_spec(PO1{})> || PointOriginFor<PO1, get_quantity_spec(PO2{})>) &&
            (is_derived_from_specialization_of_v<PO1, relative_point_origin> ||
             is_derived_from_specialization_of_v<PO2, relative_point_origin>)
[[nodiscard]]
constexpr
xref:mp_units/Quantity-0c.adoc[Quantity] auto
operator‐(
    PO1 lhs,
    PO2 rhs);
----

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

== Return Value

[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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