[Surfacing Hidden Design: A Better Alternative To Interrelated Mutable Fields](http://wp.me/p3ui6n-1q) - 1) Explicit and defect-preventing expression of the states and transitions - full code

EpidemySimulator_PrimitiveFull.scala

  // P.S.: Excuse the underscores ...
  class Person (val id: Int) {

    // Simplified primitive version, assuming the information when should the evolution
    // happen is handled somewhere else
    def evolveHealth(): Unit = {
      if (!_infected)
        if (randomGenerator.randomBelow(101) <= config.transmissibilityPct)
          this._infected = true
      if (_infected && !_sick && !_immune)
        this._sick = true
      if (_sick)
        if (randomGenerator.randomBelow(101) <= config.mortalityPct)
          this._dead = true
        else
          this._unDead = true // did not die but still sick
      if (_unDead)
        this._immune = true
        this._sick = true
      if (_immune)
        this._immune = false
        this._infected = false
    }
    
    private var _unDead = false
    private var _infected = false
    private var _sick = false
    private var _immune = false
    private var _dead = false
  }