Add valueIn method (#185)

src/measure/__test__/numberMeasureTests.ts

@@ -287,6 +287,12 @@ describe("Number measures", () => {
             expect(Measure.of(1000, meters).in(kilometers)).toBe("1000 m");
         });
 
+        it("should get value in another unit", () => {
+            const kilometers = Measure.of(1000, meters);
+            expect(Measure.of(2000, meters).valueIn(kilometers)).toBe(2);
+            expect(Measure.of(500, meters).valueIn(kilometers)).toBe(0.5);
+        });
+
         it("should use base unit symbols to format when available", () => {
             const m = Measure.dimension("test-length", "meter");
             const s = Measure.dimension("test-time", "second");

src/measure/genericMeasure.ts

@@ -193,6 +193,14 @@ export interface GenericMeasure<N, U extends Unit> {
      */
     in(unit: GenericMeasure<N, U>, formatter?: MeasureFormatter<N>): string;
 
+    /**
+     * Returns the value of this measure as a product of another unit. This can be used to quickly convert a measure to
+     * that unit and extract its underlying value.
+     * @param unit a measure of the same unit to convert this measure into
+     * @returns the numeric value of this unit expressed in the given unit
+     */
+    valueIn(unit: GenericMeasure<N, U>): N;
+
     /**
      * Adds a symbol to this measure.
      * @param symbol the symbol of the unit represented by this measure

src/measure/genericMeasureClass.ts

@@ -147,6 +147,10 @@ export function createMeasureClass<N>(num: NumericOperations<N>): GenericMeasure
             return `${value} ${unit.symbol}`;
         }
 
+        public valueIn(unit: GenericMeasure<N, U>): N {
+            return num.div(this.value, unit.value);
+        }
+
         public withSymbol(symbol: string | undefined): GenericMeasure<N, U> {
             return new Measure(this.value, this.unit, symbol);
         }

test/measures.ts → test/measureTypeTests.ts

@@ -58,3 +58,9 @@ area.minus(volume);
 
 // TODO(jscheinerman): This should be an error but is not because of structural typing
 length.plus(velocity);
+
+// TODO(jscheinerman): This should be an error but is not because of structural typing
+length.valueIn(velocity);
+
+// TODO(jscheinerman): This should be an error but is not because of structural typing
+export const test: Length = velocity;