Add combinations of Density, Area, and LinearDensity operators

UnitsNet.Tests/CustomCode/AreaTests.cs

@@ -51,6 +51,13 @@ public void AreaTimesMassFluxEqualsMassFlow()
             Assert.Equal(massFlow, MassFlow.FromKilogramsPerSecond(40));
         }
 
+        [Fact]
+        public void AreaTimesDensityEqualsLinearDensity()
+        {
+            LinearDensity linearDensity = Area.FromSquareCentimeters(2) * Density.FromGramsPerCubicCentimeter(10);
+            Assert.Equal(LinearDensity.FromGramsPerCentimeter(20), linearDensity);
+        }
+
         [Theory]
         [InlineData(0, 0)]
         [InlineData(0.5, 0.19634954084936208)]

UnitsNet.Tests/CustomCode/DensityTests.cs

@@ -121,5 +121,12 @@ public void DensityTimesAccelerationEqualsSpecificWeight()
             SpecificWeight specificWeight = Density.FromKilogramsPerCubicMeter(10) * Acceleration.FromMetersPerSecondSquared(2);
             Assert.Equal(SpecificWeight.FromNewtonsPerCubicMeter(20), specificWeight);
         }
+
+        [Fact]
+        public void DensityTimesAreaEqualsLinearDensity()
+        {
+            LinearDensity linearDensity = Density.FromGramsPerCubicCentimeter(10) * Area.FromSquareCentimeters(2);
+            Assert.Equal(LinearDensity.FromGramsPerCentimeter(20), linearDensity);
+        }
     }
 }

UnitsNet.Tests/CustomCode/LinearDensityTests.cs

@@ -22,6 +22,7 @@
 
 
 using System;
+using Xunit;
 
 namespace UnitsNet.Tests.CustomCode
 {
@@ -47,6 +48,19 @@ public class LinearDensityTests : LinearDensityTestsBase
         protected override double PoundsPerInchInOneKilogramPerMeter => 5.599741459E-02;
 
         protected override double PoundsPerFootInOneKilogramPerMeter => 6.71968975e-1;
-
+
+        [Fact]
+        public void LinearDensityDividedByAreaEqualsDensity()
+        {
+            Density density = LinearDensity.FromGramsPerCentimeter(10) / Area.FromSquareCentimeters(2);
+            Assert.Equal(Density.FromGramsPerCubicCentimeter(5), density);
+        }
+
+        [Fact]
+        public void LinearDensityDividedByDensityEqualsArea()
+        {
+            Area area = LinearDensity.FromGramsPerCentimeter(10) / Density.FromGramsPerCubicCentimeter(2);
+            Assert.Equal(Area.FromSquareCentimeters(5), area);
+        }
     }
 }

UnitsNet/CustomCode/Quantities/Area.extra.cs

@@ -41,5 +41,11 @@ public static Area FromCircleRadius(Length radius)
         {
             return VolumeFlow.FromCubicMetersPerSecond(area.SquareMeters * speed.MetersPerSecond);
         }
+
+        /// <summary>Get <see cref="LinearDensity"/> from <see cref="Area"/> times <see cref="Density"/>.</summary>
+        public static LinearDensity operator *(Area area, Density density)
+        {
+            return LinearDensity.FromKilogramsPerMeter(area.SquareMeters * density.KilogramsPerCubicMeter);
+        }
     }
 }

UnitsNet/CustomCode/Quantities/Density.extra.cs

@@ -70,5 +70,11 @@ public static Density FromMolarity(Molarity molarity, Mass molecularWeight)
         {
             return new Molarity(density.KilogramsPerCubicMeter / molecularWeight.Kilograms, MolarityUnit.MolesPerCubicMeter);
         }
+
+        /// <summary>Get <see cref="LinearDensity"/> from <see cref="Density"/> times <see cref="Area"/>.</summary>
+        public static LinearDensity operator *(Density density, Area area)
+        {
+            return LinearDensity.FromKilogramsPerMeter(density.KilogramsPerCubicMeter * area.SquareMeters);
+        }
     }
 }

UnitsNet/CustomCode/Quantities/LinearDensity.extra.cs

@@ -0,0 +1,21 @@
+// Licensed under MIT No Attribution, see LICENSE file at the root.
+// Copyright 2013 Andreas Gullberg Larsen (andreas.larsen84@gmail.com). Maintained at https://github.com/angularsen/UnitsNet.
+
+namespace UnitsNet
+{
+    public partial struct LinearDensity
+    {
+
+        /// <summary>Get <see cref="Density"/> from <see cref="LinearDensity"/> times <see cref="Area"/>.</summary>
+        public static Density operator /(LinearDensity linearDensity, Area area)
+        {
+            return Density.FromKilogramsPerCubicMeter(linearDensity.KilogramsPerMeter / area.SquareMeters);
+        }
+
+        /// <summary>Get <see cref="Area"/> from <see cref="LinearDensity"/> times <see cref="Density"/>.</summary>
+        public static Area operator /(LinearDensity linearDensity, Density density)
+        {
+            return Area.FromSquareMeters(linearDensity.KilogramsPerMeter / density.KilogramsPerCubicMeter);
+        }
+    }
+}