Add molality quantity

Author: crystal-growth

src/si/mod.rs

@@ -102,6 +102,7 @@ system! {
         mass_density::MassDensity,
         mass_flux::MassFlux,
         mass_rate::MassRate,
+        molality::Molality,
         molar_concentration::MolarConcentration,
         molar_energy::MolarEnergy,
         molar_flux::MolarFlux,

src/si/molality.rs

@@ -0,0 +1,51 @@
+//! Molality (base unit mole per kilogram, kg⁻¹ · mol).
+
+quantity! {
+    /// Molality (base unit mole per kilogram, kg⁻¹ · mol).
+    quantity: Molality; "molality";
+    /// Dimension of molality, M⁻¹N (base unit mole per kilogram, kg⁻¹ · mol).
+    dimension: ISQ<
+        Z0,     // length
+        N1,     // mass
+        Z0,     // time
+        Z0,     // electric current
+        Z0,     // thermodynamic temperature
+        P1,     // amount of substance
+        Z0>;    // luminous intensity
+    kind: dyn (crate::si::marker::ConstituentConcentrationKind);
+
+    units {
+        @mole_per_kilogram: prefix!(none);
+            "mol/kg", "mole per kilogram", "moles per kilogram";
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    storage_types! {
+        use crate::num::One;
+        use crate::si::amount_of_substance as aos;
+        use crate::si::mass as m;
+        use crate::si::molality as mol;
+        use crate::si::quantities::*;
+        use crate::tests::Test;
+
+        #[test]
+        fn check_dimension() {
+            let _: Molality<V> = (AmountOfSubstance::new::<aos::mole>(V::one())
+                / Mass::new::<m::kilogram>(V::one())).into();
+        }
+
+        #[test]
+        fn check_units() {
+
+            test::<aos::mole, m::kilogram,  mol::mole_per_kilogram>();
+
+            fn test<AOS: aos::Conversion<V>, M: m::Conversion<V>, MOL: mol::Conversion<V>>() {
+                Test::assert_approx_eq(&Molality::new::<MOL>(V::one()),
+                    &(AmountOfSubstance::new::<AOS>(V::one()) / 
+                    Mass::new::<M>(V::one())).into());
+            }
+        }
+    }
+}