Normalize Temperature arithmetic

Common/UnitDefinitions/Temperature.json

@@ -2,7 +2,6 @@
   "Name": "Temperature",
   "BaseUnit": "Kelvin",
   "XmlDoc": "A temperature is a numerical measure of hot or cold. Its measurement is by detection of heat radiation or particle velocity or kinetic energy, or by the bulk behavior of a thermometric material. It may be calibrated in any of various temperature scales, Celsius, Fahrenheit, Kelvin, etc. The fundamental physical definition of temperature is provided by thermodynamics.",
-  "GenerateArithmetic": false,
   "BaseDimensions": {
     "Θ": 1
   },
@@ -104,4 +103,4 @@
       ]
     }
   ]
-}
+}

UnitsNet.Tests/CustomCode/TemperatureDeltaTests.cs

@@ -1,9 +1,9 @@
 //------------------------------------------------------------------------------
 // <auto-generated>
 //     This code was generated (once) by \generate-code.bat, but will not be
-//     regenerated when it already exists. The purpose of creating this file is to make 
+//     regenerated when it already exists. The purpose of creating this file is to make
 //     it easier to remember to implement all the unit conversion test cases.
-// 
+//
 //     Whenever a new unit is added to this unit class and \generate-code.bat is run,
 //     the base test class will get a new abstract property and cause a compile error
 //     in this derived class, reminding the developer to implement the test case
@@ -19,17 +19,17 @@
 
 // Copyright (c) 2013 Andreas Gullberg Larsen ([email protected]).
 // https://github.com/angularsen/UnitsNet
-// 
+//
 // Permission is hereby granted, free of charge, to any person obtaining a copy
 // of this software and associated documentation files (the "Software"), to deal
 // in the Software without restriction, including without limitation the rights
 // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 // copies of the Software, and to permit persons to whom the Software is
 // furnished to do so, subject to the following conditions:
-// 
+//
 // The above copyright notice and this permission notice shall be included in
 // all copies or substantial portions of the Software.
-// 
+//
 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
@@ -38,6 +38,8 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 // THE SOFTWARE.
 using System;
+using System.Globalization;
+using UnitsNet.Units;
 using Xunit;
 
 namespace UnitsNet.Tests.CustomCode
@@ -59,5 +61,24 @@ public void TemperatureDeltaTimesSpecificEntropyEqualsSpecificEnergy()
             SpecificEnergy specificEnergy =  SpecificEntropy.FromJoulesPerKilogramKelvin(10) * TemperatureDelta.FromKelvins(6);
             Assert.Equal(specificEnergy, SpecificEnergy.FromJoulesPerKilogram(60));
         }
+
+        [Theory]
+        [InlineData(TemperatureUnit.DegreeCelsius, 30, 20, "10 ∆°C")]
+        [InlineData(TemperatureUnit.DegreeCelsius, 20, 30, "-10 ∆°C")]
+        [InlineData(TemperatureUnit.DegreeFahrenheit, 30, 20, "10 ∆°F")]
+        [InlineData(TemperatureUnit.DegreeFahrenheit, 20, 30, "-10 ∆°F")]
+        [InlineData(TemperatureUnit.Kelvin, 30, 20, "10 ∆K")]
+        [InlineData(TemperatureUnit.Kelvin, 20, 30, "-10 ∆K")]
+        public void FromTemperatures_ReturnsDeltaOfTheTwoTemperaturesInLeftUnit(TemperatureUnit unit, int value, int otherValue, string expected)
+        {
+            Temperature temperature = Temperature.From(value, unit);
+            Temperature otherTemperature = Temperature.From(otherValue, unit);
+
+            // Act
+            var delta = TemperatureDelta.FromTemperatures(temperature, otherTemperature);
+
+            // Assert
+            Assert.Equal(expected, delta.ToString(CultureInfo.InvariantCulture, "{0:0} {1}"));
+        }
     }
 }

UnitsNet.Tests/CustomCode/TemperatureTests.cs

@@ -1,16 +1,16 @@
 // Copyright (c) 2013 Andreas Gullberg Larsen ([email protected]).
 // https://github.com/angularsen/UnitsNet
-// 
+//
 // Permission is hereby granted, free of charge, to any person obtaining a copy
 // of this software and associated documentation files (the "Software"), to deal
 // in the Software without restriction, including without limitation the rights
 // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 // copies of the Software, and to permit persons to whom the Software is
 // furnished to do so, subject to the following conditions:
-// 
+//
 // The above copyright notice and this permission notice shall be included in
 // all copies or substantial portions of the Software.
-// 
+//
 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
@@ -45,46 +45,6 @@ public class TemperatureTests : TemperatureTestsBase
 
         protected override double KelvinsInOneKelvin => 1;
 
-        [SuppressMessage("ReSharper", "ImpureMethodCallOnReadonlyValueField",
-            Justification = "R# incorrectly identifies method as impure, due to internal method calls.")]
-        [Theory]
-        [InlineData(TemperatureUnit.DegreeCelsius, 10, 1, "10 °C")]
-        [InlineData(TemperatureUnit.DegreeCelsius, 10, 5, "2 °C")]
-        [InlineData(TemperatureUnit.DegreeCelsius, 10, -10, "-1 °C")]
-        [InlineData(TemperatureUnit.DegreeFahrenheit, 10, 1, "10 °F")]
-        [InlineData(TemperatureUnit.DegreeFahrenheit, 10, 5, "2 °F")]
-        [InlineData(TemperatureUnit.DegreeFahrenheit, 10, -10, "-1 °F")]
-        public void DividedByTemperatureDeltaEqualsTemperature(TemperatureUnit unit, int temperatureVal, int divisor, string expected)
-        {
-            Temperature temperature = Temperature.From(temperatureVal, unit);
-
-            // Act
-            Temperature resultTemp = temperature.Divide(divisor, unit);
-
-            string actual = resultTemp.ToUnit(unit).ToString(CultureInfo.InvariantCulture, "{0:0} {1}");
-            Assert.Equal(expected, actual);
-        }
-
-        [SuppressMessage("ReSharper", "ImpureMethodCallOnReadonlyValueField",
-            Justification = "R# incorrectly identifies method as impure, due to internal method calls.")]
-        [Theory]
-        [InlineData(TemperatureUnit.DegreeCelsius, 10, 0, "0 °C")]
-        [InlineData(TemperatureUnit.DegreeCelsius, 10, 5, "50 °C")]
-        [InlineData(TemperatureUnit.DegreeCelsius, 10, -5, "-50 °C")]
-        [InlineData(TemperatureUnit.DegreeFahrenheit, 10, 0, "0 °F")]
-        [InlineData(TemperatureUnit.DegreeFahrenheit, 10, 5, "50 °F")]
-        [InlineData(TemperatureUnit.DegreeFahrenheit, 10, -5, "-50 °F")]
-        public void MultiplyByTemperatureDeltaEqualsTemperature(TemperatureUnit unit, int temperatureVal, int factor, string expected)
-        {
-            Temperature temperature = Temperature.From(temperatureVal, unit);
-
-            // Act
-            Temperature resultTemp = temperature.Multiply(factor, unit);
-
-            string actual = resultTemp.ToUnit(unit).ToString(CultureInfo.InvariantCulture, "{0:0} {1}");
-            Assert.Equal(expected, actual);
-        }
-
         [Theory]
         [InlineData(TemperatureUnit.DegreeCelsius, -10, 0, "-10 °C")]
         [InlineData(TemperatureUnit.DegreeCelsius, -10, 10, "0 °C")]
@@ -141,5 +101,24 @@ public void TemperaturePlusTemperatureDeltaEqualsTemperature(TemperatureUnit uni
             string actual = resultTemp.ToUnit(unit).ToString(CultureInfo.InvariantCulture, "{0:0} {1}");
             Assert.Equal(expected, actual);
         }
+
+        [Theory]
+        [InlineData(TemperatureUnit.DegreeCelsius, 30, 20, "10 ∆°C")]
+        [InlineData(TemperatureUnit.DegreeCelsius, 20, 30, "-10 ∆°C")]
+        [InlineData(TemperatureUnit.DegreeFahrenheit, 30, 20, "10 ∆°F")]
+        [InlineData(TemperatureUnit.DegreeFahrenheit, 20, 30, "-10 ∆°F")]
+        [InlineData(TemperatureUnit.Kelvin, 30, 20, "10 ∆K")]
+        [InlineData(TemperatureUnit.Kelvin, 20, 30, "-10 ∆K")]
+        public void ToDelta_ReturnsDeltaOfTwoTemperaturesInSameUnit(TemperatureUnit unit, int value, int otherValue, string expected)
+        {
+            Temperature temperature = Temperature.From(value, unit);
+            Temperature otherTemperature = Temperature.From(otherValue, unit);
+
+            // Act
+            var delta = temperature.ToDelta(otherTemperature);
+
+            // Assert
+            Assert.Equal(expected, delta.ToString(CultureInfo.InvariantCulture, "{0:0} {1}"));
+        }
     }
 }

UnitsNet/CustomCode/Quantities/Temperature.extra.cs

@@ -1,16 +1,16 @@
 // Copyright (c) 2013 Andreas Gullberg Larsen ([email protected]).
 // https://github.com/angularsen/UnitsNet
-// 
+//
 // Permission is hereby granted, free of charge, to any person obtaining a copy
 // of this software and associated documentation files (the "Software"), to deal
 // in the Software without restriction, including without limitation the rights
 // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 // copies of the Software, and to permit persons to whom the Software is
 // furnished to do so, subject to the following conditions:
-// 
+//
 // The above copyright notice and this permission notice shall be included in
 // all copies or substantial portions of the Software.
-// 
+//
 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
@@ -36,7 +36,7 @@ public partial struct Temperature
         // Windows Runtime Component does not allow operator overloads: https://msdn.microsoft.com/en-us/library/br230301.aspx
 #if !WINDOWS_UWP
         /// <summary>
-        ///     Add a <see cref="Temperature" /> and a <see cref="TemperatureDelta" />.
+        ///     Add a <see cref="TemperatureDelta" /> to a <see cref="Temperature" />.
         /// </summary>
         /// <remarks>Due to temperature units having different scales, the arithmetic must be performed on the same scale.</remarks>
         /// <returns>The new temperature.</returns>
@@ -46,7 +46,7 @@ public partial struct Temperature
         }
 
         /// <summary>
-        ///     Add a <see cref="TemperatureDelta" /> and a <see cref="Temperature" />.
+        ///     Add a <see cref="TemperatureDelta" /> to a <see cref="Temperature" />.
         /// </summary>
         /// <remarks>Due to temperature units having different scales, the arithmetic must be performed on the same scale.</remarks>
         /// <returns>The new temperature.</returns>
@@ -56,7 +56,7 @@ public partial struct Temperature
         }
 
         /// <summary>
-        ///     Subtract a <see cref="Temperature" /> by a <see cref="TemperatureDelta" />.
+        ///     Subtract a <see cref="TemperatureDelta" /> from a <see cref="Temperature" />.
         /// </summary>
         /// <remarks>Due to temperature units having different scales, the arithmetic must be performed on the same scale.</remarks>
         /// <returns>The new temperature.</returns>
@@ -66,49 +66,15 @@ public partial struct Temperature
         }
 
         /// <summary>
-        ///     Subtract a <see cref="Temperature" /> by a <see cref="TemperatureDelta" />.
+        ///     Subtract two temperatures to get a <see cref="TemperatureDelta"/> in this temperature's unit, which you can later convert to any temperature unit.
+        ///     This is useful since Celsius, Fahrenheit and Kelvins don't share a common zero point on the scale and normal subtraction
+        ///     would operate on Kelvins and likely give an unexpected result.
+        ///     Example:
+        ///     double deltaCelsius = celsius30.ToDelta(celsius20).DegreesCelsius; // 10 C
+        ///     double wrongDeltaCelsius = (celsius30 - celsius20).DegreesCelsius; // 303.15 K - 293.15 K = 10 K = -263.15 degrees Celsius
         /// </summary>
-        /// <remarks>Due to temperature units having different scales, the arithmetic must be performed on the same scale.</remarks>
-        /// <returns>The delta temperature (difference).</returns>
-        public static TemperatureDelta operator -(Temperature left, Temperature right)
-        {
-            return new TemperatureDelta(left.Kelvins - right.Kelvins, TemperatureDeltaUnit.Kelvin);
-        }
+        /// <returns>A temperature delta.</returns>
+        public TemperatureDelta ToDelta(Temperature other) => TemperatureDelta.FromTemperatures(this, other);
 #endif
-
-        /// <summary>
-        ///     Multiply temperature with a <paramref name="factor" /> in a given <paramref name="unit" />.
-        /// </summary>
-        /// <remarks>
-        ///     Due to different temperature units having different zero points, we cannot simply
-        ///     multiply or divide a temperature by a factor. We must first convert to the desired unit, then perform the
-        ///     calculation.
-        /// </remarks>
-        /// <param name="factor">Factor to multiply by.</param>
-        /// <param name="unit">Unit to perform multiplication in.</param>
-        /// <returns>The resulting <see cref="Temperature" />.</returns>
-        public Temperature Multiply(double factor, TemperatureUnit unit)
-        {
-            double resultInUnit = As(unit) * factor;
-            return From(resultInUnit, unit);
-        }
-
-
-        /// <summary>
-        ///     Divide temperature by a <paramref name="divisor" /> in a given <paramref name="unit" />.
-        /// </summary>
-        /// <remarks>
-        ///     Due to different temperature units having different zero points, we cannot simply
-        ///     multiply or divide a temperature by a factor. We must first convert to the desired unit, then perform the
-        ///     calculation.
-        /// </remarks>
-        /// <param name="divisor">Factor to multiply by.</param>
-        /// <param name="unit">Unit to perform multiplication in.</param>
-        /// <returns>The resulting <see cref="Temperature" />.</returns>
-        public Temperature Divide(double divisor, TemperatureUnit unit)
-        {
-            double resultInUnit = As(unit) / divisor;
-            return From(resultInUnit, unit);
-        }
     }
 }

UnitsNet/CustomCode/Quantities/TemperatureDelta.extra.cs

@@ -20,6 +20,10 @@
 // THE SOFTWARE.
 
 // ReSharper disable once CheckNamespace
+
+using System;
+using UnitsNet.Units;
+
 namespace UnitsNet
 {
     // Windows Runtime Component has constraints on public types: https://msdn.microsoft.com/en-us/library/br230301.aspx#Declaring types in Windows Runtime Components
@@ -47,6 +51,32 @@ public partial struct TemperatureDelta
         {
             return specificEntropy * temperatureDelta;
         }
+
+        /// <summary>
+        ///     Subtract two temperatures to get a <see cref="TemperatureDelta"/> in <paramref name="left"/>'s unit, which you can later convert to any temperature unit.
+        ///     This is useful since Celsius, Fahrenheit and Kelvins don't share a common zero point on the scale and normal subtraction
+        ///     would operate on Kelvins and likely give an unexpected result.
+        ///     Example:
+        ///     double deltaCelsius = TemperatureDelta.FromTemperatures(celsius30, celsius20).DegreesCelsius; // 10 C
+        ///     double wrongDeltaCelsius = (celsius30 - celsius20).DegreesCelsius; // 303.15 K - 293.15 K = 10 K = -263.15 degrees Celsius
+        /// </summary>
+        /// <returns>A temperature delta.</returns>
+        public static TemperatureDelta FromTemperatures(Temperature left, Temperature right)
+        {
+            TemperatureDeltaUnit deltaUnit = ToDeltaUnit(left.Unit);
+            return new TemperatureDelta(left.Value - right.As(left.Unit), deltaUnit);
+        }
+
+        /// <summary>
+        /// Converts a temperature unit to a temperature delta unit.
+        /// They share the exact same unit names, but are of different enum types and have slightly different semantic meaning.
+        /// </summary>
+        /// <param name="temperatureUnit">Temperature unit.</param>
+        /// <returns>Equivalent temperature delta unit.</returns>
+        public static TemperatureDeltaUnit ToDeltaUnit(TemperatureUnit temperatureUnit)
+        {
+            return (TemperatureDeltaUnit)Enum.Parse(typeof(TemperatureDeltaUnit), temperatureUnit.ToString());
+        }
 #endif
     }
 }