Redesign UnitSystem to support non-SI systems and configurable default units

CodeGen/Generators/UnitsNetGen/QuantityGenerator.cs

@@ -183,23 +183,25 @@ private void GenerateInstanceConstructors()
         /// <param name=""value"">The numeric value to construct this quantity with.</param>
         /// <param name=""unitSystem"">The unit system to create the quantity with.</param>
         /// <exception cref=""ArgumentNullException"">The given <see cref=""UnitSystem""/> is null.</exception>
-        /// <exception cref=""ArgumentException"">No unit was found for the given <see cref=""UnitSystem""/>.</exception>
+        /// <exception cref=""ArgumentException"">No default unit was found for the given <see cref=""UnitSystem""/>.</exception>
         public {_quantity.Name}({_valueType} value, UnitSystem unitSystem)
         {{
-            if(unitSystem == null) throw new ArgumentNullException(nameof(unitSystem));
-
-            var unitInfos = Info.GetUnitInfosFor(unitSystem.BaseUnits);
-            var firstUnitInfo = unitInfos.FirstOrDefault();
+            if(unitSystem == null) throw new ArgumentNullException(nameof(unitSystem)); 
 ");
 
             Writer.WL(_quantity.BaseType == "double"
                 ? @"
-            _value = Guard.EnsureValidNumber(value, nameof(value));"
+            _value = Guard.EnsureValidNumber(value, nameof(value));
+"
                 : @"
-            _value = value;");
-            Writer.WL(@"
-            _unit = firstUnitInfo?.Value ?? throw new ArgumentException(""No units were found for the given UnitSystem."", nameof(unitSystem));
-        }
+            _value = value;
+");
+
+            Writer.WL($@"
+            var defaultUnitInfo = unitSystem.GetDefaultUnitInfo(QuantityType) as UnitInfo<{_unitEnumName}>;
+
+            _unit = defaultUnitInfo?.Value ?? throw new ArgumentException(""No default unit was defined for the given UnitSystem."", nameof(unitSystem));
+        }}
 ");
         }
 
@@ -821,13 +823,12 @@ public double As(UnitSystem unitSystem)
             if(unitSystem == null)
                 throw new ArgumentNullException(nameof(unitSystem));
 
-            var unitInfos = Info.GetUnitInfosFor(unitSystem.BaseUnits);
+            var defaultUnitInfo = unitSystem.GetDefaultUnitInfo(QuantityType) as UnitInfo<{_unitEnumName}>;
 
-            var firstUnitInfo = unitInfos.FirstOrDefault();
-            if(firstUnitInfo == null)
-                throw new ArgumentException(""No units were found for the given UnitSystem."", nameof(unitSystem));
+            if(defaultUnitInfo == null)
+                throw new ArgumentException(""No default unit was found for the given UnitSystem."", nameof(unitSystem));
 
-            return As(firstUnitInfo.Value);
+            return As(defaultUnitInfo.Value);
         }}
 
         /// <inheritdoc />
@@ -864,13 +865,12 @@ IQuantity IQuantity.ToUnit(Enum unit)
             if(unitSystem == null)
                 throw new ArgumentNullException(nameof(unitSystem));
 
-            var unitInfos = Info.GetUnitInfosFor(unitSystem.BaseUnits);
+            var defaultUnitInfo = unitSystem.GetDefaultUnitInfo(QuantityType) as UnitInfo<{_unitEnumName}>;
 
-            var firstUnitInfo = unitInfos.FirstOrDefault();
-            if(firstUnitInfo == null)
-                throw new ArgumentException(""No units were found for the given UnitSystem."", nameof(unitSystem));
+            if(defaultUnitInfo == null)
+                throw new ArgumentException(""No default unit was found for the given UnitSystem."", nameof(unitSystem));
 
-            return ToUnit(firstUnitInfo.Value);
+            return ToUnit(defaultUnitInfo.Value);
         }}
 
         /// <inheritdoc />

UnitsNet.Tests/CustomCode/LengthTests.cs

@@ -4,6 +4,7 @@
 using Xunit;
 using UnitsNet.Units;
 using System;
+using System.Linq;
 
 namespace UnitsNet.Tests.CustomCode
 {
@@ -186,6 +187,16 @@ public void Constructor_UnitSystemSI_AssignsSIUnit()
             Assert.Equal(LengthUnit.Meter, length.Unit);
         }
 
+        [Fact]
+        public void Constructor_UnitSystemMySmallSI_AssignsMillimiters()
+        {
+            var myDefaultLengthUnit = Length.Info.UnitInfos.First(x => x.Value == LengthUnit.Millimeter);
+            var myUnitSystem = UnitSystem.SI.WithDefaultUnit(QuantityType.Length, myDefaultLengthUnit);
+
+            var length = new Length(1.0, myUnitSystem);
+            Assert.Equal(LengthUnit.Millimeter, length.Unit);
+        }
+
         [Fact]
         public void Constructor_UnitSystemWithNoMatchingBaseUnits_ThrowsArgumentException()
         {

UnitsNet.Tests/UnitSystemTests.cs

@@ -2,6 +2,7 @@
 // Copyright 2013 Andreas Gullberg Larsen (andreas.larsen84@gmail.com). Maintained at https://github.com/angularsen/UnitsNet.
 
 using System;
+using System.Linq;
 using UnitsNet.Units;
 using Xunit;
 
@@ -149,5 +150,55 @@ public void SIUnitSystemHasCorrectBaseUnits()
             Assert.Equal(AmountOfSubstanceUnit.Mole, UnitSystem.SI.BaseUnits.Amount);
             Assert.Equal(LuminousIntensityUnit.Candela, UnitSystem.SI.BaseUnits.LuminousIntensity);
         }
+
+        [Fact]
+        public void GetDefaultUnitInfoThrowsExceptionForUndefinedQuantity()
+        {
+            Assert.Throws<ArgumentException>(() => UnitSystem.SI.GetDefaultUnitInfo(QuantityType.Undefined));
+        }
+
+        [Fact]
+        public void GetDefaultUnitInfoReturnsNullForQuantitiesWithNoDefaultUnits()
+        {
+            // TODO do we expect to preserve this behavior?
+            // AmplitudeRatio might be unitless- but there are (more than one) ways to express ratios. 
+            Assert.Null(UnitSystem.SI.GetDefaultUnitInfo(AmplitudeRatio.QuantityType));
+        }
+
+        [Fact]
+        public void WithDefaultUnitThrowsIfQuantityTypeIsUndefined()
+        {
+            Assert.Throws<ArgumentException>(() => UnitSystem.SI.WithDefaultUnit(QuantityType.Undefined, null));
+        }
+
+        [Fact]
+        public void WithDefaultUnitUsesOldBaseUnitsIfNotSpecified()
+        {
+            var myDefaultLengthUnit = Length.Info.UnitInfos.First(x => x.Value == LengthUnit.Millimeter);
+
+            var newSI = UnitSystem.SI.WithDefaultUnit(QuantityType.Length, myDefaultLengthUnit, (BaseUnits) null); 
+
+            Assert.Equal(UnitSystem.SI, newSI); // currently comparing using BaseUnits
+        }
+
+        [Theory]
+        [InlineData(LengthUnit.Undefined, MassUnit.Kilogram, DurationUnit.Second, ElectricCurrentUnit.Ampere, TemperatureUnit.Kelvin, AmountOfSubstanceUnit.Mole, LuminousIntensityUnit.Candela)]
+        [InlineData(LengthUnit.Meter, MassUnit.Undefined, DurationUnit.Second, ElectricCurrentUnit.Ampere, TemperatureUnit.Kelvin, AmountOfSubstanceUnit.Mole, LuminousIntensityUnit.Candela)]
+        [InlineData(LengthUnit.Meter, MassUnit.Kilogram, DurationUnit.Undefined, ElectricCurrentUnit.Ampere, TemperatureUnit.Kelvin, AmountOfSubstanceUnit.Mole, LuminousIntensityUnit.Candela)]
+        [InlineData(LengthUnit.Meter, MassUnit.Kilogram, DurationUnit.Second, ElectricCurrentUnit.Undefined, TemperatureUnit.Kelvin, AmountOfSubstanceUnit.Mole, LuminousIntensityUnit.Candela)]
+        [InlineData(LengthUnit.Meter, MassUnit.Kilogram, DurationUnit.Second, ElectricCurrentUnit.Ampere, TemperatureUnit.Undefined, AmountOfSubstanceUnit.Mole, LuminousIntensityUnit.Candela)]
+        [InlineData(LengthUnit.Meter, MassUnit.Kilogram, DurationUnit.Second, ElectricCurrentUnit.Ampere, TemperatureUnit.Kelvin, AmountOfSubstanceUnit.Undefined, LuminousIntensityUnit.Candela)]
+        [InlineData(LengthUnit.Meter, MassUnit.Kilogram, DurationUnit.Second, ElectricCurrentUnit.Ampere, TemperatureUnit.Kelvin, AmountOfSubstanceUnit.Mole, LuminousIntensityUnit.Undefined)]
+        public void WithDefaultUnitThrowsIfSpecifiedBaseUnitsNotFullyDefined(LengthUnit length, MassUnit mass, DurationUnit time, ElectricCurrentUnit current,
+            TemperatureUnit temperature, AmountOfSubstanceUnit amount, LuminousIntensityUnit luminousIntensity)
+        {
+            var myDefaultLengthUnit = Length.Info.UnitInfos.First(x => x.Value == LengthUnit.Millimeter);
+
+            var baseUnits = new BaseUnits(length, mass, time, current, temperature, amount, luminousIntensity);
+
+            // TODO do we want to preserve this behavior?
+            Assert.Throws<ArgumentException>(()=> UnitSystem.SI.WithDefaultUnit(QuantityType.Length, myDefaultLengthUnit, baseUnits));
+        }
+
     }
 }