Crate yaiouom

Units of measure.

This crate implements a mechanism of units of measure. It may be used to manipulate all sorts of measures, including physics/engineering (m, kg, s, A, m * s ^ 1, ...), currencies (EUR, USD, ...), statistics (dollars per barrel, engineers per lightbulb, dollars per household per year, ...)

While this is not the first implementation of units of measure in Rust, this is the first one that is both extensible (you can trivially add new base units), compositional (two units defined in different crates may interact without trouble) and type-safe (the compiler will inform you if you attempt to mix several incompatible units of measure without converting them first). However, before using this crate, please read the rest of these explanations.

Unification and the companion linter

At the time of this writing, the Rust type system is not powerful enough to permit an extensible, compositional, type-safe representation of units of measure. For this reason, other crates implementing units of measure have needed to make a choice:

• either prevent compositional extensibility;
• or give up on type safety.

This crate uses a different approach, by delegating safety checks to a specialized checker, yaiouom-checker. This checker extends Rust's type system with a mechanism ensuring that units of measure are used safely.

If you do not use the checker, you'll end up with a binary that performs (slow) dynamic unit checking in debug builds, and no unit checking in optimized builds.

The linter guarantees that you'll never hit such dynamic panics.

You really should use the companion linter :) Also, please see the documentation of unify.

Representation of values

Different values have different rules. Many are f32 or f64, but currency computations, for instance, need to be performed with either rationals or fixed point arithmetics. Some electrical measures are actually complex values. Statistics may use integer values for population, etc.

For this reason, yaiouom does not hardcode a specific representation of values. A value with a unit is a Measure<T, U: Unit>, where T can be any kind of number or number-like value.

Limitations

As discussed above,

Please use the companion linter! Also, please see the documentation of unify.

This crate attempts to be strictly minimal.

Unit conversion is a complicated thing. We do not attempt to solve this problem.

Some values cannot be multiplied or divided (e.g. ºC, ºF, pH, dB). We do not attempt to differentiate between units that can be multiplied/dived and units that can, although this might happen in a future version.

Some values have different definitions when subtracted. For instance, the difference between two dates in seconds is a duration in seconds. The difference between two ºC temperatures is a value that may be multiplied or divided. We do not attempt to differentiate between these things.

Modules

si	International system of units.

Structs

Dimensionless	A unit without dimension.
Inv	The inverse of a unit of measure.
Measure	A value with a unit.
Mul	The product of two units of measure.
RuntimeUnit	Runtime representation of a unit.

Traits

BaseUnit	A base unit of measure (e.g. meters, euros, ...)
Unit	A unit of measure.