[#mp_units-quantity_cast-0b]
= xref:mp_units.adoc[mp_units]::quantity_cast
:relfileprefix: ../
:mrdocs:

Explicit cast of a quantity 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 FwdQ,
    xref:mp_units/Quantity.adoc[Quantity] Q = std::remove_cvref_t<FwdQ>>
requires (castable(Q::quantity_spec, ToQS)) && (MP_UNITS_WEAK_UNIT_OF(MP_UNITS_NONCONST_TYPE(Q::unit), ToQS))
[[nodiscard]]
constexpr
xref:mp_units/Quantity.adoc[Quantity] auto
quantity_cast(FwdQ&& q);
----

== Description

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

For example:

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

====

== Template Parameters

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


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