[wpiunits] Add Measure.divide(Measure<U2>) (#6611)

wpiunits/src/main/java/edu/wpi/first/units/Measure.java

@@ -137,16 +137,29 @@ public interface Measure<U extends Unit<U>> extends Comparable<Measure<U>> {
   }
 
   /**
-   * Divides this measurement by some constant divisor and returns the result. This is equivalent to
-   * {@code divide(divisor.baseUnitMagnitude())}
+   * Divides this measurement by another measure and performs some dimensional analysis to reduce
+   * the units.
    *
-   * @param divisor the dimensionless measure to divide by
+   * @param <U2> the type of the other measure to multiply by
+   * @param other the unit to multiply by
    * @return the resulting measure
-   * @see #divide(double)
-   * @see #times(double)
    */
-  default Measure<U> divide(Measure<Dimensionless> divisor) {
-    return divide(divisor.baseUnitMagnitude());
+  default <U2 extends Unit<U2>> Measure<?> divide(Measure<U2> other) {
+    if (unit().getBaseUnit().equals(other.unit().getBaseUnit())) {
+      return Units.Value.ofBaseUnits(baseUnitMagnitude() / other.baseUnitMagnitude());
+    }
+    if (other.unit() instanceof Dimensionless) {
+      return divide(other.baseUnitMagnitude());
+    }
+    if (other.unit() instanceof Velocity<?> velocity
+        && velocity.getUnit().getBaseUnit().equals(unit().getBaseUnit())) {
+      return times(velocity.reciprocal().ofBaseUnits(1 / other.baseUnitMagnitude()));
+    }
+    if (other.unit() instanceof Per<?, ?> per
+        && per.numerator().getBaseUnit().equals(unit().getBaseUnit())) {
+      return times(per.reciprocal().ofBaseUnits(1 / other.baseUnitMagnitude()));
+    }
+    return unit().per(other.unit()).ofBaseUnits(baseUnitMagnitude() / other.baseUnitMagnitude());
   }
 
   /**

wpiunits/src/main/java/edu/wpi/first/units/Per.java

@@ -109,6 +109,15 @@ public class Per<N extends Unit<N>, D extends Unit<D>> extends Unit<Per<N, D>> {
     return m_denominator;
   }
 
+  /**
+   * Returns the reciprocal of this Per.
+   *
+   * @return the reciprocal
+   */
+  public Per<D, N> reciprocal() {
+    return m_denominator.per(m_numerator);
+  }
+
   @Override
   public boolean equals(Object o) {
     if (this == o) {

wpiunits/src/main/java/edu/wpi/first/units/Velocity.java

@@ -157,6 +157,15 @@ public class Velocity<D extends Unit<D>> extends Unit<Velocity<D>> {
     return m_period;
   }
 
+  /**
+   * Returns the reciprocal of this velocity.
+   *
+   * @return the reciprocal
+   */
+  public Per<Time, D> reciprocal() {
+    return m_period.per(m_unit);
+  }
+
   @Override
   public boolean equals(Object o) {
     if (this == o) {

wpiunits/src/test/java/edu/wpi/first/units/EncoderTest.java

@@ -7,7 +7,6 @@ package edu.wpi.first.units;
 import static edu.wpi.first.units.Units.Inches;
 import static edu.wpi.first.units.Units.Revolutions;
 import static edu.wpi.first.units.Units.Second;
-import static edu.wpi.first.units.Units.Value;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
 import org.junit.jupiter.api.Test;
@@ -46,14 +45,14 @@ class EncoderTest {
 
   @Test
   void testAsDistance() {
-    var ticksPerRevolution = Value.of(2048);
+    double ticksPerRevolution = 2048;
 
     var encoder = new Encoder<Distance>();
 
     // distance per rotation = (wheel circumference / gear ratio)
     // distance per tick = distance per rotation / ticks per rotation
     var wheelDiameter = Inches.of(6);
-    var gearRatio = Value.of(10); // 10:1 ratio
+    double gearRatio = 10; // 10:1 ratio
     Measure<Distance> distancePerPulse =
         wheelDiameter.times(Math.PI).divide(gearRatio).divide(ticksPerRevolution);
     encoder.setDistancePerPulse(distancePerPulse);
@@ -74,7 +73,7 @@ class EncoderTest {
 
   @Test
   void testAsRevolutions() {
-    var ticksPerRevolution = Value.of(2048);
+    double ticksPerRevolution = 2048;
 
     var encoder = new Encoder<Angle>();
 

wpiunits/src/test/java/edu/wpi/first/units/MeasureTest.java

@@ -162,6 +162,40 @@ class MeasureTest {
     assertEquals(exampleUnit.of(42 * 17 / (12 * 25.4)), m3.times(m4));
   }
 
+  @Test
+  void testDivideMeasure() {
+    // Dimensionless divide
+    var m1 = Units.Meters.of(6);
+    var m2 = Units.Value.of(3);
+    var result = m1.divide(m2);
+    assertEquals(m1.divide(m2).magnitude(), 2);
+    assertEquals(result.unit(), Units.Meters);
+    // Velocity divide
+    var m3 = Units.Meters.of(8);
+    var m4 = Units.Meters.per(Units.Second).of(4);
+    result = m3.divide(m4);
+    assertEquals(result.magnitude(), 2);
+    assertEquals(result.unit(), Units.Second);
+    // Per divide
+    var m5 = Units.Volts.of(6);
+    var m6 = Units.Volts.per(Units.Meter).of(2);
+    result = m5.divide(m6);
+    assertEquals(result.magnitude(), 3);
+    assertEquals(result.unit(), Units.Meter);
+    // Fallthrough divide
+    var m7 = Units.Seconds.of(10);
+    var m8 = Units.Amps.of(2);
+    result = m7.divide(m8);
+    assertEquals(result.magnitude(), 5);
+    assertEquals(result.unit(), Units.Seconds.per(Units.Amps));
+    // Same base unit divide
+    var m9 = Units.Meters.of(8);
+    var m10 = Units.Meters.of(4);
+    result = m9.divide(m10);
+    assertEquals(result.magnitude(), 2);
+    assertEquals(result.unit(), Units.Value);
+  }
+
   @Test
   void testToShortString() {
     var measure = Units.Volts.of(343);