Helper functions

helper.swift

import Foundation

/// This is going to be one of those things that for many of you is so obvious that it doesn't
/// require saying. But maybe a few of you have never really done this before either. I've been
/// thinking about nested helper functions.

/// I've used little nested helper functions lots of times. I do this when I want a function, but 
/// nothing outside of this scope would ever need it.
func doSomething() {
    func inc(x: Int) -> Int { return x + 1 }
    print("\(inc(2))")
}


/// And I've sometimes used the parameters to the outer function in the nested function, which is
/// often very handy. This is really common in Scala because you often need this for loops.
func doSomethingToX(x: Int) {
    func incX() -> Int { return x + 1 }
    print("\(incX())")
}


/// But I've always created the helper function at the top. I'd never thought about setting a bunch
/// of things to be captured by the helper. For example, from a current project I'm playing with:
func solve(config: Config) throws {
    let input = try config.parser(filename: config.filename)

    // Here I set up the formatter
    let formatter = NSDateComponentsFormatter()
    formatter.allowedUnits = [.Hour, .Minute, .Second]

    // And here I set the start date
    let startDate = NSDate()

    // And *then* I define the helper function, which makes the rest of the code much simpler
    func duration() -> NSString {
        return formatter.stringFromDate(startDate, toDate: NSDate()) ?? ""
    }

    var bestSolution: Solution?
    for solution in GeneratorSequence(config.makeSolutionGenerator(input)) {
        bestSolution = solution
        print("\(duration()) : \(solution.progressOutput)")
    }
    print("Final Time: \(duration())")
    print("")
    print(bestSolution?.finalOutput ?? "NO SOLUTION")
}