macro_rules! quantity { ( $(#[$quantity_attr:meta])* quantity: $quantity:ident; $description:expr; $(#[$dim_attr:meta])* dimension: $system:ident<$($dimension:ident),+>; $(kind: $kind:ty;)? units { $($(#[$unit_attr:meta])* @$unit:ident: $($conversion:expr),+; $abbreviation:expr, $singular:expr, $plural:expr;)+ } ) => { ... }; (@kind $kind:ty) => { ... }; (@kind) => { ... }; }
Expand description
Macro to implement a quantity and associated measurement units. Note
that this macro must be executed in direct submodules of the module where the system!
macro
was executed. @...
match arms are considered private.
$quantity_attr
: Quantity attributes. Generally used to set documentation comments for the quantity.$quantity
: Quantity name (e.g.Length
).$description
: Quantity description (e.g."length"
).$dim_attr
: Dimension attributes. Generally used to set documentation comments for the quantity’s dimension type alias.$system
: System of quantities type (e.g.ISQ
).$dimension
: Power of a factor for each base quantity in the system. Power should be represented as atypenum
type-level integer (e.g.N1
,Z0
,P1
,P2
, …).$kind
: Kind of the quantity. Optional. This variable should only be specified when defining a quantity that has the same dimensions as another quantity but isn’t comparable. When not specifiedcrate::Kind
is used.$unit
: Unit name (e.g.meter
,foot
).$conversion
: Conversion (coefficient and constant factor) from the unit to the base unit of the quantity (e.g.3.048_E-1
to convertfoot
tometer
.1.0_E0, 273.15_E0
to convertcelsius
tokelvin
.). The coefficient is required and the constant factor is optional. Note that using a unit with a non-zero constant factor is not currently supported as a base unit.$abbreviation
: Unit abbreviation (e.g."m"
).$singular
: Singular unit description (e.g."meter"
).$plural
: Plural unit description (e.g."meters"
).
An example invocation is given below for the quantity of length in a meter-kilogram-second
system. The #[macro_use]
attribute must be used when including the uom
crate to make the
quantity!
macro available.
#[macro_use]
extern crate uom;
#[macro_use]
mod length {
quantity! {
/// Length (base unit meter, m).
quantity: Length; "length";
/// Length dimension, m.
dimension: Q<P1 /*length*/, Z0 /*mass*/, Z0 /*time*/>;
units {
@meter: 1.0E0; "m", "meter", "meters";
@foot: 3.048E-1; "ft", "foot", "feet";
}
}
}