Merge pull request #332 from crystal-growth/add_electric_permittivity

Add ElectricPermittivity with related units.

src/si/electric_permittivity.rs

@@ -0,0 +1,50 @@
+//! Electric permittivity (base unit farad per meter, m⁻³ · kg⁻¹ · s⁴ · A²).
+
+quantity! {
+    /// Electric permittivity (base unit farad per meter, m⁻³ · kg⁻¹ · s⁴ · A²).
+    quantity: ElectricPermittivity; "electric permittivity";
+    /// Dimension of electric permittivity, L⁻³M⁻¹T⁴I² (base unit farad per meter,
+    /// m⁻³ · kg⁻¹ · s⁴ · A²).
+    dimension: ISQ<
+        N3,     // length
+        N1,     // mass
+        P4,     // time
+        P2,     // electric current
+        Z0,     // thermodynamic temperature
+        Z0,     // amount of substance
+        Z0>;    // luminous intensity
+    units {
+        @farad_per_meter: prefix!(none); "F/m", "farad per meter", "farads per meter";
+        @vacuum_electric_permittivity: 8.854_187_8128_E-12; "ε₀", "vacuum electric permittivity",
+            "vacuum electric permittivity";
+    }
+}
+
+#[cfg(test)]
+mod test {
+    storage_types! {
+        use crate::num::One;
+        use crate::si::capacitance as c;
+        use crate::si::electric_permittivity as ep;
+        use crate::si::length as l;
+        use crate::si::quantities::*;
+        use crate::tests::Test;
+
+        #[test]
+        fn check_dimension() {
+            let _: ElectricPermittivity<V> = Capacitance::new::<c::farad>(V::one())
+                / Length::new::<l::meter>(V::one());
+        }
+
+        #[test]
+        fn check_units() {
+            test::<ep::farad_per_meter, c::farad, l::meter>();
+
+            fn test<EP: ep::Conversion<V>, C: c::Conversion<V>, L: l::Conversion<V>>() {
+                Test::assert_approx_eq(&ElectricPermittivity::new::<EP>(V::one()),
+                    &(Capacitance::new::<C>(V::one())
+                        / Length::new::<L>(V::one())));
+            }
+        }
+    }
+}

src/si/mod.rs

@@ -62,6 +62,7 @@ system! {
         dynamic_viscosity::DynamicViscosity,
         electric_charge::ElectricCharge,
         electric_current::ElectricCurrent,
+        electric_permittivity::ElectricPermittivity,
         electric_potential::ElectricPotential,
         electrical_conductance::ElectricalConductance,
         electrical_conductivity::ElectricalConductivity,