Unit conversions about dimensioned HOT 3 CLOSED

// Define Quantity<D, B, V> where D is the dimensions, B is the base units, and V is the value type.
pub struct Quantity<D, B, V> {
    value: V,
    dimensions: PhantomData<D>,
    base_units: PhantomData<B>,
}

// Define SI<> system with the seven dimensions of quantities.
...

// Define  Standard as the SI base units (m, kg, s, A, K, mol, cd) for the base
// quantities (length, mass, ...). This would be something similar to your From
// trait implementation
...

// Type alias desired base and derived quantities. Note that these aren't specific
// units such as meter or foot.
pub type Length<V> = Quantity<SI<P1, Z0, Z0, Z0, Z0, Z0, Z0>, Standard, V>;
pub type Mass<V> = Quantity<SI<Z0, P1, Z0, Z0, Z0, Z0, Z0>, Standard, V>;
...
pub type Force<V> = Quantity<SI<P1, Z0, N2, Z0, Z0, Z0, Z0>, Standard, V>;

// Define conversion factors, unit descriptions, and abbreviations for quantities
// defined above.
pub trait Conversion<V, U> {
    pub fn to_base(value: V, unit: U) -> V; // Converts value in unit to the base unit.
    pub fn _from_base(value: V, unit: U) -> V; // Converts value in the base unit to unit.
}

define_conversions!(Length
    meter: 1.0, "meter", "m";
    kilometer: Prefix.kilo, "kilometer", "km";
    foot: 3.048E-1, "foot", "f";
    inch: 2.54E-2, "inch", "in";
    ...);

define_conversions!(Mass ...);
...
define_conversions!(Force ...);

// Usage.
use dimensioned::si::f32::{Length, Time, Velocity};

// Raw values, from the user or untyped libraries, need to be lifted into appropriate
// dimensioned types:
let length1 = 100.0 * yard; // Length::new(100.0, yard);
let length2 = 100.0 * meter; // Length::new(100.0, meter);
let time = 100.0 * second; // Time::new(100.0, second);

// Once setup all formulas can be done using appropriate quantities and no effort
// needs to be put into unit conversions or dimensional analysis. The compiler catches
// impossible formulas.
let length3 = length1 + length2;
let velocity1 = length1 / time;
let velocity2 = length2 / time;
//let invalid = length1 + time; // mismatched types [E0308]

// Accessing a specific unit (ex. kilometer, foot, ...) is possible but shouldn't be done until
// a quantity is being persisted or displayed to the user.
let feet: f32 = length3.get(foot); // Discouraged.
println!(/*<format specifier saying value should be displayed in kilometers per
    hour and include the unit's abbreviation>*/, velocity1); // outputs 3.291 km/h