5 Quantities and units library [quantities]

5.6 Quantity [qty]

5.6.5 Constructors and assignment [qty.cons]

template<typename FwdValue, Reference R2>
  requires SameValueAs<R2{}, R, std::remove_cvref_t<FwdValue>, Rep>
constexpr quantity(FwdValue&& v, R2);

template<ValuePreservingTo<Rep> FwdValue>
  requires(unit == ::mp_units::one)
constexpr quantity(FwdValue&& v);

Effects: Initializes numerical-value with std::forward<FwdValue>(v).

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template<typename FwdValue, Reference R2, typename Value = std::remove_cvref_t<FwdValue>>
  requires(!SameValueAs<R2{}, R, Value, Rep>) &&
          QuantityConvertibleTo<quantity<R2{}, Value>, quantity>
constexpr quantity(FwdValue&& v, R2);

Effects: Equivalent to quantity(quantity<R2{}, Value>{std::forward<FwdValue>(v), R2{}}).

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template<QuantityConvertibleTo<quantity> Q>
constexpr explicit(!std::convertible_to<typename Q::rep, Rep>) quantity(const Q& q);

Effects: Equivalent to sudo-cast<quantity>(q) ([qty.non.mem.conv]).

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template<QuantityLike Q>
  requires QuantityConvertibleTo<quantity-like-type<Q>, quantity>
constexpr explicit(see below) quantity(const Q& q);

Effects: Equivalent to: quantity(::mp_units::quantity{quantity_like_traits<Q>::to_numerical_value(q), quantity_like_traits<Q>::reference})

Remarks: The expression inside explicit is equivalent to: quantity_like_traits<Q>::explicit_import || !std::convertible_to<typename quantity_like_traits<Q>::rep, Rep>

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template<ValuePreservingTo<Rep> FwdValue>
  requires(unit == ::mp_units::one)
constexpr quantity& operator=(FwdValue&& v);

Effects: Equivalent to numerical-value = std::forward<FwdValue>(v).

Returns: *this.