[#mp_units-value_cast-02e]
= xref:mp_units.adoc[mp_units]::value_cast
:relfileprefix: ../
:mrdocs:

Explicit cast of a quantity's unit and representation type

== Synopsis

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

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    xref:mp_units/Unit.adoc[Unit] auto ToU,
    typename ToRep,
    typename FwdQ,
    xref:mp_units/Quantity.adoc[Quantity] Q = std::remove_cvref_t<FwdQ>>
requires (MP_UNITS_WEAK_UNIT_OF(MP_UNITS_REMOVE_CONST(decltype(ToU)), Q::quantity_spec)) &&
          RepresentationOf<ToRep, Q::quantity_spec> && std::constructible_from<ToRep, typename Q::rep> &&
          detail::SaneScaling<Q::unit, ToU, ToRep>
[[nodiscard]]
constexpr
xref:mp_units/Quantity.adoc[Quantity] auto
value_cast(FwdQ&& q);
----

== Description

Implicit conversions between quantities of different types are allowed only for "safe" (e.g. non‐truncating) conversion. In truncating cases an explicit cast have to be used.

auto q = value_cast<us, int>(1.23 * ms);

== Template Parameters

[cols=2]
|===
| Name
| Description
| *ToU*
| a unit to use for the target quantity
| *ToRep*
| a representation type to use for the target quantity
|===


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