[#mp_units-value_cast-027]
= xref:mp_units.adoc[mp_units]::value_cast
:relfileprefix: ../
:mrdocs:

Explicit cast of a quantity point's unit

== 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 FwdQP,
    xref:mp_units/QuantityPoint.adoc[QuantityPoint] QP = std::remove_cvref_t<FwdQP>>
requires (MP_UNITS_WEAK_UNIT_OF(MP_UNITS_REMOVE_CONST(decltype(ToU)), QP::quantity_spec)) &&
          detail::SaneScaling<QP::unit, ToU, typename QP::rep>
[[nodiscard]]
constexpr
xref:mp_units/QuantityPoint.adoc[QuantityPoint] auto
value_cast(FwdQP&& qp);
----

== Description

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

auto qp = value_cast<si::second>(quantity_point{1234 * ms});

== Template Parameters

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


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