performance_chaining.swift

// Swift
let sum = fahrenheit.map({ (degreesFahrenheit) -> Double in
    return (degreesFahrenheit - 32.0) / 1.8
}).filter({ (degreesCelsius) -> Bool in
    return degreesCelsius <= 20.0
}).reduce(0.0) { (result, degreesCelsius) -> Double in
    return result + degreesCelsius
}

// For-in loop
var sum: Double = 0.0
        
for degreesFahrenheit in fahrenheit {
    let degreesCelsius = (degreesFahrenheit - 32.0) / 1.8
    if degreesCelsius <= 20.0 {
        sum += degreesCelsius
    }
}