oriches / Simple.Units

Units of measure for the world, does not contain all units or all conversions just the ones I wanted at the time - it can be expanded...

Simple.Units

As with all my 'important' stuff it builds using the amazing AppVeyor.

This is how I would model 'units of measure' in a system, this came out of discussion around building a system which required the ability to convert between different units of distance.

The easiest way to demostrate is with a unit test:

 [Test]
  public void one_metre_is_one_hundred_centimetres()
  {
    // ARRANGE
    var measurementInMetres = new Measurement(1d, Units.Metre);

    // ACT
    var measurementInCentimetres = measurementInMetres.ConvertTo(Units.Centimetre);

    // ASSERT
     Assert.That(measurementInCentimetres.Amount, Is.EqualTo(100d));
  }

Put simply the unit test creates a metre measurement and then converts this into a cenitmetre measurement and checks the conversion from 1 metre to 100 centimetres was correct.

Hopefuilly what you can see is there are 3 class involved here - Measurement, Units & Unit:

Measurement

Contains the actual measured value and units (of measure) - represents the measurement.

The important\interesting part is the ConvertTo method, as the name says it invokes the conversion, but does not actual do the conversion, this is the responiblity of the Unit instance.

Unit

Defines a 'unit of measure' as being a Name, an Abrevation and set of Conversions to other units. Makes use of lazy initialisation\evaluation for converters to allow circular references be built in the code, eh?

read on...

Units

Defines the set of 'unit of measure' I want\need in the system, and importantly defines the conversions between them. This is where the lazy initialisation\evaluation comes into play, if I hadn't used Lazy<T> for this it would have failed at compile time becuase there are circular references defined in the conversions.

e.g kilometre -> metre -> centimetre -> kilometre -> centimetre etc..

 public readonly static Unit Centimetre = new Unit("Centimetre", "cm", new LazyConversions(() => new Dictionary<Unit, Func<double, double>>
 {
   { Metre, value => value / 100d },
   { Kilometre, value => (value / 100d) / 1000d }
 }));

 public readonly static Unit Metre = new Unit("Metre", "m", new LazyConversions(() => new Dictionary<Unit, Func<double, double>>
 {
   { Centimetre, value => value * 100d },
   { Kilometre, value => value / 1000d }
 }));

 public readonly static Unit Kilometre = new Unit("Kilometre", "km", new LazyConversions(() => new Dictionary<Unit, Func<double, double>>
 {
   { Metre, value => value * 1000d },
   { Mile, value => value / 1.609344d }
 }));

Happy coding...