Temperature units as abstract type

The following Celcius and Fahrenheit Abstract types are based on the underlying Float type, but sets the restriction that it can never hold values below absolute zero.

Also, the @:to field casts take care of automatically converting from one unit to the other.

abstract Celcius(Float) to Float {    
  inline function new(value : Float)  
    this = Math.max(value, -273.15);
    
  @:from inline static public function fromFloat(value : Float) : Celcius
    return new Celcius(value);    
    
  // the following field cast automatically converts to Fahrenheit from Celcius
  @:to inline public function toFahrenheit() : Fahrenheit    
    return (this / 5 * 9) + 32;   
}

abstract Fahrenheit(Float) to Float {    
  inline function new(value : Float)  
    this = Math.max(value, -459.67);
    
  @:from inline static public function fromFloat(value : Float) : Fahrenheit
    return new Fahrenheit(value);      
  
  // the following field cast automatically converts to Celcius from Fahrenheit
  @:to inline public function toCelcius() : Celcius
    return (this - 32) * 5 / 9;
}

Usage

// Here we start by defining a temperature in Celcius
var waterfreezeC:Celcius = 0;
trace('Water freezes at $waterfreezeC degrees Celcius.');   

// Please note the unit conversion in the following line, automatically 
// invoking the Celcius.toFahrenheit() method for us:
var waterfreezeF:Fahrenheit = waterfreezeC;        
trace('Water freezes at $waterfreezeF degrees Fahrenheit.');   

Credits to Franco Ponticelli

This example is inspired by Franco Ponticelli's Thx.Unit library. There, you can find lots of interesting examples of well written code using abstract types. To point out one intersting thing: In thx.unit, the temperature abstracts are based on another abstract type - Decimal - for greater floating point accuracy.

Learn about Haxe Abstracts here: https://haxe.org/manual/types-abstract.html