prefix_postfix.swift

postfix operator ~~~

struct Engine {
    var tank: Float
    var consumption: Float
    var distance: Float
    var consumptionTarget: Float?
    
    static prefix func ~ (engine: Engine) -> Engine {
        return Engine(tank: engine.tank,
                      consumption: engine.consumption,
                      distance: engine.distance,
                      consumptionTarget: engine.distance / engine.tank)
    }
    
    static postfix func ~~~ (engine: Engine) -> Engine {
        return Engine(tank: engine.tank,
                      consumption: engine.consumption,
                      distance: engine.tank / engine.consumption * 100,
                      consumptionTarget: engine.consumptionTarget)
    }
    
}

let truck = Engine(tank: 400.0, consumption: 20.0, distance: 1300.0, consumptionTarget: nil)
let calculatedTruck = ~truck

print("target: \(String(describing: calculatedTruck.consumptionTarget))")
/*
 target: Optional(3.25)
 */

let maxDistanceTruck = truck~~~

print("max distance: \(String(describing: maxDistanceTruck.distance))")
/*
 max distance: 2000.0
 */