[#mp_units-quantity-01-2constructor-06a]
= xref:mp_units.adoc[mp_units]::xref:mp_units/quantity-01.adoc[quantity]::quantity
:relfileprefix: ../../
:mrdocs:

Constructors

== Synopses

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

Default constructor. Leaves the numerical value default‐initialized.


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
[[nodiscard]]
xref:mp_units/quantity-01/2constructor-062.adoc[quantity]() = default;
----

[.small]#xref:mp_units/quantity-01/2constructor-062.adoc[_» more..._]#

Converting constructor from another quantity that shares an equivalent unit.


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    auto R2,
    typename Rep2>
requires detail::QuantityConstructibleFrom<quantity, quantity<R2, Rep2>> && (equivalent(unit, get_unit(R2)))
[[nodiscard]]
constexpr
explicit(!std::convertible_to<Rep2, rep> || !mp_units::implicitly_convertible(get_quantity_spec(R2), quantity_spec) || !mp_units::implicitly_scalable<get_unit(R2), Rep2, unit, rep>)
xref:mp_units/quantity-01/2constructor-07.adoc[quantity](xref:mp_units/quantity-01.adoc[quantity<R2, Rep2>] const& q);
----

[.small]#xref:mp_units/quantity-01/2constructor-07.adoc[_» more..._]#

Converting constructor from another quantity whose unit needs scaling to this one.


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    auto R2,
    typename Rep2>
requires detail::QuantityConstructibleFrom<quantity, quantity<R2, Rep2>> && (!equivalent(unit, get_unit(R2)))
[[nodiscard]]
constexpr
explicit(!std::convertible_to<Rep2, rep> || !mp_units::implicitly_convertible(get_quantity_spec(R2), quantity_spec) || !mp_units::implicitly_scalable<get_unit(R2), Rep2, unit, rep>)
xref:mp_units/quantity-01/2constructor-067.adoc[quantity](xref:mp_units/quantity-01.adoc[quantity<R2, Rep2>] const& q);
----

[.small]#xref:mp_units/quantity-01/2constructor-067.adoc[_» more..._]#

Constructs a quantity directly from a numerical value, without an explicit reference.


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
[[nodiscard]]
constexpr
explicit(!mp_units::implicitly_convertible(quantity_spec, dimensionless))
xref:mp_units/quantity-01/2constructor-0c.adoc[quantity](xref:mp_units/quantity-01/rep.adoc[rep] val)
requires detail::ExplicitFromNumber<reference>;
----

[.small]#xref:mp_units/quantity-01/2constructor-0c.adoc[_» more..._]#

Constructs a quantity from a value convertible to `rep`, without an explicit reference.


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<typename Value>
requires detail::ExplicitFromNumber<reference> && detail::RepConstructibleFrom<rep, Value> &&
             (!std::convertible_to<Value, rep>)
[[nodiscard]]
constexpr
explicit
xref:mp_units/quantity-01/2constructor-09.adoc[quantity](Value val);
----

[.small]#xref:mp_units/quantity-01/2constructor-09.adoc[_» more..._]#

Deleted overload that rejects truncating conversions when constructing without a reference.


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<typename Value>
requires detail::ExplicitFromNumber<reference> && (!detail::RepConstructibleFrom<rep, Value>)
constexpr
explicit(!std::convertible_to<Value, rep> || !mp_units::implicitly_convertible(quantity_spec, dimensionless))
xref:mp_units/quantity-01/2constructor-0f0.adoc[quantity](Value val) = delete;
----

[.small]#xref:mp_units/quantity-01/2constructor-0f0.adoc[_» more..._]#

Constructs a quantity from an external quantity‐like type via `quantity_like_traits`.


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<xref:mp_units/QuantityLike.adoc[QuantityLike] Q>
requires detail::QuantityConstructibleFrom<quantity, detail::quantity_like_type<Q>>
[[nodiscard]]
constexpr
explicit(quantity_like_traits<Q>::explicit_import || !std::convertible_to<detail::quantity_like_type<Q>, quantity<R, Rep>>)
xref:mp_units/quantity-01/2constructor-08.adoc[quantity](Q const& q);
----

[.small]#xref:mp_units/quantity-01/2constructor-08.adoc[_» more..._]#

Constructs a quantity from a numerical value and a reference with an equivalent unit.


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<xref:mp_units/Reference-0ba.adoc[Reference] R2>
requires (equivalent(unit, get_unit(R2{})))
[[nodiscard]]
constexpr
xref:mp_units/quantity-01/2constructor-0f8.adoc[quantity](
    xref:mp_units/quantity-01/rep.adoc[rep] val,
    R2 ref);
----

[.small]#xref:mp_units/quantity-01/2constructor-0f8.adoc[_» more..._]#

Deleted overload that rejects truncating conversions of the numerical value.


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    typename Value,
    xref:mp_units/Reference-0ba.adoc[Reference] R2>
requires (equivalent(unit, get_unit(R2{}))) && (!detail::RepConstructibleFrom<rep, Value>)
constexpr
xref:mp_units/quantity-01/2constructor-0fc.adoc[quantity](
    Value val,
    R2 ref) = delete;
----

[.small]#xref:mp_units/quantity-01/2constructor-0fc.adoc[_» more..._]#

Constructs a quantity from a numerical value and a reference with a different unit.


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    typename FwdValue,
    xref:mp_units/Reference-0ba.adoc[Reference] R2>
requires (!equivalent(unit, get_unit(R2{}))) &&
            detail::QuantityConstructibleFrom<quantity, quantity<R2{}, std::remove_cvref_t<FwdValue>>>
[[nodiscard]]
constexpr
xref:mp_units/quantity-01/2constructor-0b.adoc[quantity](
    FwdValue&& val,
    R2 ref);
----

[.small]#xref:mp_units/quantity-01/2constructor-0b.adoc[_» more..._]#

== Parameters

[cols="1,4"]
|===
| Name| Description
| *q*
| the source quantity to convert from
| *val*
| the numerical value to store
| *ref*
| a reference whose unit is equivalent to `unit`
|===


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