[#mp_units-quantity_cast-05]
= xref:mp_units.adoc[mp_units]::quantity_cast
:relfileprefix: ../
:mrdocs:

Explicit cast of a quantity point type

== Synopsis

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

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    xref:mp_units/QuantitySpec.adoc[QuantitySpec] auto ToQS,
    typename FwdQP,
    xref:mp_units/QuantityPoint.adoc[QuantityPoint] QP = std::remove_cvref_t<FwdQP>>
requires (castable(QP::quantity_spec, ToQS)) && (MP_UNITS_WEAK_UNIT_OF(MP_UNITS_NONCONST_TYPE(QP::unit), ToQS))
[[nodiscard]]
constexpr
xref:mp_units/QuantityPoint.adoc[QuantityPoint] auto
quantity_cast(FwdQP&& qp);
----

== Description

This cast converts only a quantity point type. It might be used to force some quantity point type conversions that are not implicitly allowed but are allowed explicitly.

For example:

[,cpp]
----
{.cpp}
 auto length = isq::length(quantity_point{42 * m});
 auto altitude = quantity_cast<isq::altitude>(length);
----
[NOTE]
====
This cast does not affect the underlying value of a number stored in a quantity point&period;

====

== Template Parameters

[cols=2]
|===
| Name
| Description
| *ToQS*
| a quantity specification to use for a target quantity point
|===


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