Add IValueQuantity<TValue> interface to expose the value type

CodeGen/Generators/UnitsNetGen/QuantityGenerator.cs

@@ -263,20 +263,10 @@ private void GenerateProperties()
         ///     The numeric value this quantity was constructed with.
         /// </summary>
         public {_valueType} Value => _value;
-");
 
-            Writer.WL(@"
         /// <inheritdoc />
         QuantityValue IQuantity.Value => _value;
-");
-            // Need to provide explicit interface implementation for decimal quantities like Information
-            if (_quantity.ValueType == "decimal")
-                Writer.WL(@"
-        /// <inheritdoc cref=""IDecimalQuantity.Value""/>
-        decimal IDecimalQuantity.Value => _value;
-");
 
-            Writer.WL($@"
         Enum IQuantity.Unit => Unit;
 
         /// <inheritdoc />
@@ -959,6 +949,15 @@ double IQuantity.As(Enum unit)
             return (double)As(typedUnit);
         }}
 
+        /// <inheritdoc />
+        {_quantity.ValueType} IValueQuantity<{_quantity.ValueType}>.As(Enum unit)
+        {{
+            if (!(unit is {_unitEnumName} typedUnit))
+                throw new ArgumentException($""The given unit is of type {{unit.GetType()}}. Only {{typeof({_unitEnumName})}} is supported."", nameof(unit));
+
+            return As(typedUnit);
+        }}
+
         /// <summary>
         ///     Converts this {_quantity.Name} to another {_quantity.Name} with the unit representation <paramref name=""unit"" />.
         /// </summary>

CodeGen/Generators/UnitsNetGen/UnitTestBaseClassGenerator.cs

@@ -164,7 +164,7 @@ public void DefaultCtor_ReturnsQuantityWithZeroValueAndBaseUnit()
             var quantity = new {_quantity.Name}();
             Assert.Equal(0, quantity.Value);");
             if (_quantity.ValueType == "decimal") Writer.WL(@"
-            Assert.Equal(0m, ((IDecimalQuantity)quantity).Value);");
+            Assert.Equal(0m, ((IValueQuantity<decimal>)quantity).Value);");
             Writer.WL($@"
             Assert.Equal({_baseUnitFullName}, quantity.Unit);
         }}
@@ -278,7 +278,7 @@ public void As_SIUnitSystem_ThrowsArgumentExceptionIfNotSupported()
 
             if (SupportsSIUnitSystem)
             {{
-                var value = (double) AsWithSIUnitSystem();
+                var value = Convert.ToDouble(AsWithSIUnitSystem());
                 Assert.Equal(1, value);
             }}
             else

Common/UnitDefinitions/Power.json

@@ -12,6 +12,11 @@
     {
       "SingularName": "Watt",
       "PluralName": "Watts",
+      "BaseUnits": {
+        "L": "Meter",
+        "M": "Kilogram",
+        "T": "Second"
+      },
       "FromUnitToBaseFunc": "{x}",
       "FromBaseToUnitFunc": "{x}",
       "Prefixes": [ "Femto", "Pico", "Nano", "Micro", "Milli", "Deci", "Deca", "Kilo", "Mega", "Giga", "Tera", "Peta" ],

UnitsNet.Serialization.JsonNet/AbbreviatedUnitsConverter.cs

@@ -79,7 +79,7 @@ public override void WriteJson(JsonWriter writer, IQuantity? quantity, JsonSeria
 
             // write the 'Value' using the actual type
             writer.WritePropertyName(ValueProperty);
-            if (quantity is IDecimalQuantity decimalQuantity)
+            if (quantity is IValueQuantity<decimal> decimalQuantity)
             {
                 // cannot use `writer.WriteValue(decimalQuantity.Value)`: there is a hidden EnsureDecimalPlace(..) method call inside it that converts '123' to '123.0'
                 writer.WriteRawValue(decimalQuantity.Value.ToString(CultureInfo.InvariantCulture));
@@ -177,7 +177,7 @@ protected string GetQuantityType(IQuantity quantity)
             {
                 value = default;
             }
-            else if (quantityInfo.Zero is IDecimalQuantity)
+            else if (quantityInfo.Zero is IValueQuantity<decimal>)
             {
                 value = decimal.Parse(valueToken, CultureInfo.InvariantCulture);
             }

UnitsNet.Serialization.JsonNet/UnitsNetBaseJsonConverter.cs

@@ -181,7 +181,7 @@ protected ValueUnit ConvertIQuantity(IQuantity quantity)
         {
             quantity = quantity ?? throw new ArgumentNullException(nameof(quantity));
 
-            if (quantity is IDecimalQuantity d)
+            if (quantity is IValueQuantity<decimal> d)
             {
                 return new ExtendedValueUnit
                 {

UnitsNet.Tests/CustomCode/IQuantityTests.cs

@@ -57,5 +57,48 @@ public void ToUnit_GivenSIUnitSystem_ReturnsSIQuantity()
             Assert.Equal(0.0508, inSI.Value);
             Assert.Equal(LengthUnit.Meter, inSI.Unit);
         }
+
+
+        [Fact]
+        public void IQuantityTUnitDouble_Value_ReturnsDouble()
+        {
+            IQuantity<TemperatureUnit, double> doubleQuantity = Temperature.FromDegreesCelsius(1234.5);
+            Assert.IsType<double>(doubleQuantity.Value);
+        }
+
+        [Fact]
+        public void IQuantityTUnitDouble_AsEnum_ReturnsDouble()
+        {
+            IQuantity<TemperatureUnit, double> doubleQuantity = Temperature.FromDegreesCelsius(1234.5);
+            Assert.IsType<double>(doubleQuantity.As(TemperatureUnit.Kelvin));
+        }
+
+        [Fact]
+        public void IQuantityTUnitDouble_AsUnitSystem_ReturnsDouble()
+        {
+            IQuantity<TemperatureUnit, double> doubleQuantity = Temperature.FromDegreesCelsius(1234.5);
+            Assert.IsType<double>(doubleQuantity.As(UnitSystem.SI));
+        }
+
+        [Fact]
+        public void IQuantityTUnitDecimal_Value_ReturnsDecimal()
+        {
+            IQuantity<InformationUnit, decimal> decimalQuantity = Information.FromKilobytes(1234.5);
+            Assert.IsType<decimal>(decimalQuantity.Value);
+        }
+
+        [Fact]
+        public void IQuantityTUnitDecimal_AsEnum_ReturnsDecimal()
+        {
+            IQuantity<InformationUnit, decimal> decimalQuantity = Information.FromKilobytes(1234.5);
+            Assert.IsType<decimal>(decimalQuantity.As(InformationUnit.Byte));
+        }
+
+        [Fact]
+        public void IQuantityTUnitDecimal_AsUnitSystem_ReturnsDecimal()
+        {
+            IQuantity<PowerUnit, decimal> decimalQuantity = Power.FromMegawatts(1234.5);
+            Assert.IsType<decimal>(decimalQuantity.As(UnitSystem.SI));
+        }
     }
 }

UnitsNet.Tests/CustomCode/PowerTests.cs

@@ -8,7 +8,7 @@ namespace UnitsNet.Tests
 {
     public class PowerTests : PowerTestsBase
     {
-        protected override bool SupportsSIUnitSystem => false;
+        protected override bool SupportsSIUnitSystem => true;
         protected override decimal FemtowattsInOneWatt => 1e15m;
 
         protected override decimal GigajoulesPerHourInOneWatt => 3600e-9m;