quantity of measurable units design pattern
I am thinking through a nice pattern to be useful across domains of measurable units (ie, Length, Time) and came up with the following use case and initial classes, and of course, questions!
1) Does a Composite pattern help or complicate?
2) Should the Convert method(s) in the ComposityNode be a separate converter class?All comments appreciated. Cheers,
BerrylExample Use Case:
var inch = new ConvertableUnit("inch", 1)
var foot = new ConvertableUnit("foot", 12)
var imperialUnits = new CompositeConvertableUnit("imperial units", .024)
imperialUnits.AddChild(inch)
imperialUnits.AddChild(foot)
var meter = new ConvertableUnit("meter", 1)
var millimeter = new ConvertableUnit("millimeter ", .001)
var imperialUnits = new CompositeConvertableUnit("metric units", 1)
imperialUnits.AddChild(meter)
imperialUnits.AddChild(millimeter)
var oneInch = new Quantity(1, inch);
var oneFoot = new Quantity(1, foot);
oneFoot.ToBase() // "12 inches"
var oneMeter = new Quantity(1, meter);
oneInch.ToBase() // .024 meters
Possible Solution
ConvertableU开发者_JAVA百科nit : Node
double Rate
string Name
Quantity
ConvertableUnit Unit
double Amount
CompositeConvertableUnit : Node
ISet<ConvertableUnit> _children
ConvertableUnit BaseUnit {get{ return _children.Where(c=>c.Rate == 1).First() } }
Quantity ConvertTo(Quantity from, Quantity to)
Quantity ToBase(Quantity from);
Martin Fowler has a very well thought out model for measurements and conversions and such in Analysis Patterns. Worth reviewing. I believe he recommended a Conversion Ratio object that would handle converting from one unit to another.
F# has a concept of units of measure built in, maybe you should look into the way they implemented it.
I don't really see any benefit to using the composite pattern here. From wikipedia:
Composite allows a group of objects to be treated in the same way as a single instance of an object.
You don't need groups of converter objects, a list of converters would be enough.
As for the Convert method - I would say converting is why the class exists, to probably a good place for it.
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