Use constants instead of types from typenum to describe units (#96)

Author: prehner

CHANGELOG.md

@@ -6,6 +6,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [0.13.0] - 2026-01-06
+### Changed
+- Use const generics instead of types from `typenum` to represent units. [#95](https://github.com/itt-ustutt/quantity/pull/95)
+
 ## [0.12.2] - 2025-12-04
 ### Fixed
 - Also updated `num-dual` dependency to 0.13 to fix incorrect dependency resolution for downstream crates. [#95](https://github.com/itt-ustutt/quantity/pull/95)

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "quantity"
-version = "0.12.2"
+version = "0.13.0"
 authors = [
     "Philipp Rehner <[email protected]>",
     "Gernot Bauer <[email protected]>",
@@ -24,7 +24,6 @@ rustdoc-args = ["--html-in-header", "./src/docs-header.html"]
 members = ["si-units", "example/extend_quantity"]
 
 [dependencies]
-typenum = "1.17"
 num-traits = "0.2"
 document-features = "0.2"
 ## Use N-dimensional arrays from the [ndarray] crate as value of a quantity.

README.md

@@ -15,7 +15,7 @@ Add this to your `Cargo.toml`:
 
 ```
 [dependencies]
-quantity = "0.12"
+quantity = "0.13"
 ```
 
 ## Examples
@@ -24,7 +24,7 @@ Calculate pressure of an ideal gas.
 
 ```rust
 let temperature = 25.0 * CELSIUS;
-let volume = 1.5 * METER.powi::<P3>();
+let volume = 1.5 * METER.powi::<3>();
 let moles = 75.0 * MOL;
 let pressure = moles * RGAS * temperature / volume;
 println!("{:.5}", pressure);            // 123.94785 kPa
@@ -36,15 +36,15 @@ Calculate the gravitational pull of the moon on the earth.
 let mass_earth = 5.9724e24 * KILOGRAM;
 let mass_moon = 7.346e22 * KILOGRAM;
 let distance = 383.398 * KILO * METER;
-let force = G * mass_earth * mass_moon / distance.powi::<P2>();
+let force = G * mass_earth * mass_moon / distance.powi::<2>();
 println!("{:.5e}", force);              // 1.99208e26 N
 ```
 
 Calculate the pressure distribution in the atmosphere using the barometric formula.
 
 ```rust
 let z = Quantity::linspace(1.0 * METER, 70.0 * KILO * METER, 10);
-let g = 9.81 * METER / SECOND.powi::<P2>();
+let g = 9.81 * METER / SECOND.powi::<2>();
 let m = 28.949 * GRAM / MOL;
 let t = 10.0 * CELSIUS;
 let p0 = BAR;

build.rs

@@ -0,0 +1,75 @@
+use std::env;
+use std::fmt::Write;
+use std::fs;
+use std::path::Path;
+
+fn main() {
+    // Generate Neg, Add, Mul, Div, Sub impls for Const<const N: i8>
+    // Limiting results of operations to values within [min, max]
+
+    // range of exponents
+    // use i32 for results that would overflow i8, we will limit to min/max in loop
+    let min: i32 = -20;
+    let max: i32 = 20;
+
+    let out_dir = env::var_os("OUT_DIR").unwrap();
+    let dest_path = Path::new(&out_dir).join("const_impls.rs");
+    let mut out = String::new();
+
+    // go over all exponent combinations
+    // for each operation, limit results to min/max
+    for a in min..=max {
+        // negation
+        let neg = -a;
+        if neg >= min && neg <= max {
+            writeln!(
+                &mut out,
+                "impl Neg for Const<{a}> {{ type Output = Const<{neg}>; fn neg(self) -> Self::Output {{ Const }} }}"
+            ).unwrap();
+        }
+
+        for b in min..=max {
+            // addition
+            let sum = a + b;
+            if sum >= min && sum <= max {
+                writeln!(
+                    &mut out,
+                    "impl Add<Const<{b}>> for Const<{a}> {{ type Output = Const<{sum}>; fn add(self, _: Const<{b}>) -> Self::Output {{ Const }} }}"
+                ).unwrap();
+            }
+
+            // subtraction
+            let diff = a - b;
+            if diff >= min && diff <= max {
+                writeln!(
+                    &mut out,
+                    "impl Sub<Const<{b}>> for Const<{a}> {{ type Output = Const<{diff}>; fn sub(self, _: Const<{b}>) -> Self::Output {{ Const }} }}"
+                ).unwrap();
+            }
+
+            // multiplication
+            let mul = a * b;
+            if mul >= min && mul <= max {
+                writeln!(
+                    &mut out,
+                    "impl Mul<Const<{b}>> for Const<{a}> {{ type Output = Const<{mul}>; fn mul(self, _: Const<{b}>) -> Self::Output {{ Const }} }}"
+                ).unwrap();
+            }
+
+            // division
+            // check: don't divide by 0 and only allow for integer results
+            if b != 0 && a % b == 0 {
+                let div = a / b;
+                if div >= min && div <= max {
+                    writeln!(
+                            &mut out,
+                            "impl Div<Const<{b}>> for Const<{a}> {{ type Output = Const<{div}>; fn div(self, _: Const<{b}>) -> Self::Output {{ Const }} }}"
+                        ).unwrap();
+                }
+            }
+        }
+    }
+
+    fs::write(&dest_path, out).unwrap();
+    println!("cargo:rerun-if-changed=build.rs");
+}

src/ad.rs

@@ -1,11 +1,10 @@
-use super::Quantity;
+use super::{Diff, Quantity};
 use nalgebra::{DefaultAllocator, Dim, OMatrix, OVector, U1, allocator::Allocator};
 use num_dual::{
     Dual, Dual2, Dual2Vec, Dual3, DualNum, DualStruct, DualVec, Gradients, HyperDual, HyperDualVec,
     HyperHyperDual, Real,
 };
 use std::ops::Sub;
-use typenum::Diff;
 
 impl<D, F, T: DualStruct<D, F>, U> DualStruct<D, F> for Quantity<T, U> {
     type Real = Quantity<T::Real, U>;
@@ -338,32 +337,10 @@ where
 #[cfg(test)]
 mod test_num_dual {
     use super::*;
-    use crate::{Area, Length, METER, Temperature, Volume};
+    use crate::{Area, Length, METER, Volume};
     use approx::assert_relative_eq;
     use nalgebra::{SMatrix, SVector, vector};
     use num_dual::{Dual64, ImplicitDerivative, ImplicitFunction};
-    use typenum::{P2, P3};
-
-    struct MyArgs<D> {
-        temperature: Temperature<D>,
-    }
-
-    impl<D: DualNum<f64> + Copy> DualStruct<D, f64> for MyArgs<D> {
-        type Real = MyArgs<f64>;
-        type Inner = MyArgs<D::Inner>;
-
-        fn re(&self) -> Self::Real {
-            MyArgs {
-                temperature: self.temperature.re(),
-            }
-        }
-
-        fn from_inner(inner: &Self::Inner) -> Self {
-            MyArgs {
-                temperature: Temperature::from_inner(&inner.temperature),
-            }
-        }
-    }
 
     struct AreaImplicit;
     impl ImplicitFunction<f64> for AreaImplicit {
@@ -403,27 +380,27 @@ mod test_num_dual {
     fn test_derivative() {
         let (v, dv) = first_derivative(volume, 5.0 * METER);
         println!("{v}\t{dv:3}");
-        assert_eq!(v, 125.0 * METER.powi::<P3>());
-        assert_eq!(dv, 75.0 * METER.powi::<P2>());
+        assert_eq!(v, 125.0 * METER.powi::<3>());
+        assert_eq!(dv, 75.0 * METER.powi::<2>());
 
         let (v, dv, d2v) = second_derivative(volume, 5.0 * METER);
         println!("{v}\t{dv:3}\t\t{d2v}");
-        assert_eq!(v, 125.0 * METER.powi::<P3>(),);
-        assert_eq!(dv, 75.0 * METER.powi::<P2>(),);
+        assert_eq!(v, 125.0 * METER.powi::<3>(),);
+        assert_eq!(dv, 75.0 * METER.powi::<2>(),);
         assert_eq!(d2v, 30.0 * METER);
 
         let (v, dv_dx, dv_dh, d2v) =
             second_partial_derivative(volume2, (5.0 * METER, 20.0 * METER));
         println!("{v}\t{dv_dx:3}\t{dv_dh:3}\t{d2v}");
-        assert_eq!(v, 500.0 * METER.powi::<P3>(),);
-        assert_eq!(dv_dx, 200.0 * METER.powi::<P2>(),);
-        assert_eq!(dv_dh, 25.0 * METER.powi::<P2>(),);
+        assert_eq!(v, 500.0 * METER.powi::<3>(),);
+        assert_eq!(dv_dx, 200.0 * METER.powi::<2>(),);
+        assert_eq!(dv_dh, 25.0 * METER.powi::<2>(),);
         assert_eq!(d2v, 10.0 * METER);
 
         let (v, dv, d2v, d3v) = third_derivative(volume, 5.0 * METER);
         println!("{v}\t{dv:3}\t\t{d2v}\t{d3v}");
-        assert_eq!(v, 125.0 * METER.powi::<P3>(),);
-        assert_eq!(dv, 75.0 * METER.powi::<P2>(),);
+        assert_eq!(v, 125.0 * METER.powi::<3>(),);
+        assert_eq!(dv, 75.0 * METER.powi::<2>(),);
         assert_eq!(d2v, 30.0 * METER);
         assert_eq!(d3v.into_value(), 6.0);
     }