[#mp_units-value_cast-04]
= xref:mp_units.adoc[mp_units]::value_cast
:relfileprefix: ../
:mrdocs:

Explicit cast of a quantity's unit

== Synopsis

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

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    auto ToU,
    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)) &&
          detail::SaneScaling<Q::unit, ToU, typename Q::rep>
[[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 d = value_cast<si::second>(1234 * ms);

== Template Parameters

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


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