5 Quantities and units library [quantities]

5.4 Reference [qty.ref]

5.4.4 Unit [qty.unit]

5.4.4.5 Types [qty.unit.types]

5.4.4.5.6 Derived [qty.derived.unit]

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namespace mp_units { template<typename... Expr> struct derived-unit-impl : // exposition only unit-interface, expr-fractions<struct one, Expr...> { using base-type = derived-unit-impl; // exposition only }; template<SymbolicConstant... Expr> struct derived_unit final : derived-unit-impl<Expr...> {}; }
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derived_unit is used by the library to represent a derived unit (IEC 60050, 112-01-19).
[Example 1: using namespace si::unit_symbols; int x = m * m; // error: cannot construct from derived_unit<power<si​::​metre, 2>> int y = m * s; // error: cannot construct from derived_unit<si​::​metre, si​::​second> int z = m / s; // error: cannot construct from derived_unit<si​::​metre, per<si​::​second>> — end example]
A program that instantiates a specialization of derived_unit that is not a possible result of the library specifications is ill-formed, no diagnostic required.