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POHow to instantiate derived class from base class generically
 

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    <p>I have extended the unit converter class given in this post: <a href="https://stackoverflow.com/a/7852721/1474894">https://stackoverflow.com/a/7852721/1474894</a> This is what I have now:</p> <pre><code>public abstract class UnitBase&lt;TUnitType, TValueType&gt; where TUnitType : struct, IComparable, IConvertible, IFormattable { protected static TUnitType BaseUnit; protected static TValueType BaseValue; private static ConcurrentDictionary&lt;TUnitType, Func&lt;TValueType, TValueType&gt;&gt; ConversionsTo = new ConcurrentDictionary&lt;TUnitType, Func&lt;TValueType, TValueType&gt;&gt;(); private static ConcurrentDictionary&lt;TUnitType, Func&lt;TValueType, TValueType&gt;&gt; ConversionsFrom = new ConcurrentDictionary&lt;TUnitType, Func&lt;TValueType, TValueType&gt;&gt;(); public static TValueType Convert(TValueType value, TUnitType from, TUnitType to) { // If both From/To are the same, don't do any work. if (from.Equals(to)) return value; // Convert into the base unit, if required. var valueInBaseUnit = from.Equals(BaseUnit) ? value : ConversionsFrom[from](value); // Convert from the base unit into the requested unit, if required var valueInRequiredUnit = to.Equals(BaseUnit) ? valueInBaseUnit : ConversionsTo[to](valueInBaseUnit); return valueInRequiredUnit; } protected static void RegisterConversion(TUnitType convertToUnit, Func&lt;TValueType, TValueType&gt; conversionTo, Func&lt;TValueType, TValueType&gt; conversionFrom) { if (!ConversionsTo.TryAdd(convertToUnit, conversionTo)) throw new ArgumentException("Already exists", "convertToUnit"); if (!ConversionsFrom.TryAdd(convertToUnit, conversionFrom)) throw new ArgumentException("Already exists", "convertToUnit"); } public static string GetUnit(TUnitType unit) { var type = typeof(TUnitType); if (!type.IsEnum) { throw new ArgumentException(); } return Enums.GetEnumDescription(unit as Enum); } public TValueType InUnit(TUnitType unit) { return Convert(BaseValue, BaseUnit, unit); } } </code></pre> <p>I have concrete implementations like this:</p> <pre><code>public enum TemperatureUnit { [System.ComponentModel.Description("°C")] Celcius, [System.ComponentModel.Description("°F")] Fahrenheit } public class Temperature : UnitBase&lt;TemperatureUnit, double&gt; { static Temperature() { BaseUnit = TemperatureUnit.Celcius; RegisterConversion(TemperatureUnit.Fahrenheit, x =&gt; x * 1.8d + 32d, x =&gt; (x - 32d) / 1.8d); } private Temperature(double value) { BaseValue = value; } public static Temperature FromUnit(double value, TemperatureUnit unit) { return new Temperature(Convert(value, unit, BaseUnit)); } } </code></pre> <p>I managed to make the ToUnit method generic as part of the base class, but with the FromUnit method I now have one per concrete class (and they would all look very similar). I want to be able to do this:</p> <pre><code>Temperature temperature = Temperature.FromUnit(10, TemperatureUnit.Celcius); Pressure pressure = Pressure.FromUnit(50, PressureUnit.Bar); </code></pre> <p>...without having to implement FromUnit in each concrete class. Because it is a static method I cannot force the implementation by using an interface. I could have a public constructor in the concrete classes and have something like:</p> <pre><code>public static T FromUnit&lt;T&gt;(TValueType value, TUnitType unit) where T : new() { BaseValue = Convert(value, unit, BaseUnit); return new T(); } </code></pre> <p>But I guess it is not that nice, and I will have to go:</p> <pre><code>Temperature temperature = Temperature.FromUnit&lt;Temperature&gt;(10, TemperatureUnit.Celcius); </code></pre> <p>The <code>&lt;Temperature&gt;</code> is kind of redundant I think.</p> <p>Is it possible to implement a generic FromUnit in a better way?</p> <p><strong>Edit:</strong> Basically I want, instead of implementing FromUnit in each sub class:</p> <pre><code>public static Temperature FromUnit(double value, TemperatureUnit unit) { return new Temperature(Convert(value, unit, BaseUnit)); } public static Pressure FromUnit(double value, PressureUnit unit) { return new Pressure(Convert(value, unit, BaseUnit)); } public static Speed FromUnit(double value, SpeedUnit unit) { return new Speed(Convert(value, unit, BaseUnit)); } ... </code></pre> <p>...to put generic FromUnit in the base class.</p>
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    2. COOK, I removed the xml comments. Thanks for the tip.
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