[#mp_units-reference-0b2]
= xref:mp_units.adoc[mp_units]::reference
:relfileprefix: ../
:mrdocs:

Quantity reference type

== Synopsis

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

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    xref:mp_units/QuantitySpec.adoc[QuantitySpec] Q,
    xref:mp_units/Unit.adoc[Unit] U>
struct reference;
----

== Description

Quantity reference describes all the properties of a quantity besides its representation type.

In most cases this class template is not explicitly instantiated by the user. It is implicitly instantiated by the library's framework while binding a quantity specification with a compatible unit.

[,cpp]
----
Reference auto kmph = isq::speed[km / h];
QuantityOf<isq::speed[km / h]> auto speed = 90 * kmph;
----
The following syntaxes are not allowed&colon; `2 &sol; kmph`, `kmph &ast; 3`, `kmph &sol; 4`, `70 &ast; isq&colon;&colon;length&lsqb;km&rsqb;&sol; isq&colon;time&lsqb;h&rsqb;`&period;

== Friends

[cols="1,4"]
|===
| Name| Description
| `xref:mp_units/cbrt-0e.adoc[mp&lowbar;units::cbrt]`
| Computes the cubic root of a reference
| `xref:mp_units/sqrt-0f.adoc[mp&lowbar;units::sqrt]`
| Computes the square root of a reference
| `xref:mp_units/pow-04.adoc[mp&lowbar;units::pow]`
| Computes the value of a reference raised to the `Num&sol;Den` power
| `xref:mp_units/inverse-0b.adoc[mp&lowbar;units::inverse]`
| Computes the inverse of a reference
| `xref:mp_units/operator_slash-0d6.adoc[mp&lowbar;units::operator&sol;]`
| Divides a unit by a reference
| `xref:mp_units/operator_slash-0e.adoc[mp&lowbar;units::operator&sol;]`
| Divides a reference by a unit
| `xref:mp_units/operator_slash-0d3.adoc[mp&lowbar;units::operator&sol;]`
| Divides a reference by another reference
| `xref:mp_units/operator_star-02b.adoc[mp&lowbar;units::operator&ast;]`
| Multiplies a unit by a reference
| `xref:mp_units/operator_star-0f.adoc[mp&lowbar;units::operator&ast;]`
| Multiplies a reference by a unit
| `xref:mp_units/operator_star-05.adoc[mp&lowbar;units::operator&ast;]`
| Multiplies two references
| `xref:mp_units/operator_eq-02.adoc[mp&lowbar;units::operator&equals;&equals;]`
| Checks whether a reference is equal to a unit
| `xref:mp_units/operator_eq-07.adoc[mp&lowbar;units::operator&equals;&equals;]`
| Checks whether two references are equal
| `xref:mp_units/get_unit.adoc[mp&lowbar;units::get&lowbar;unit]`
| Returns the unit of a reference
| `xref:mp_units/get_quantity_spec-00.adoc[mp&lowbar;units::get&lowbar;quantity&lowbar;spec]`
| Returns the quantity specification of a reference whose `Q` is marked `final`
| `xref:mp_units/get_quantity_spec-0f.adoc[mp&lowbar;units::get&lowbar;quantity&lowbar;spec]`
| Returns the quantity specification of a reference
|===


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