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libdispatch efficiency tips

The libdispatch is one of the most misused API due to the way it was presented to us when it was introduced and for many years after that, and due to the confusing documentation and API. This page is a compilation of important things to know if you're going to use this library. Many references are available at the end of this document pointing to comments from Apple's very own libdispatch maintainer (Pierre Habouzit).

My take-aways are:

• You should create very few, long-lived, well-defined queues. These queues should be seen as execution contexts in your program (gui, background work, ...) that benefit from executing in parallel. An important thing to note is that if these queues are all active at once, you will get as many threads running. In most apps, you probably do not need to create more than 3 or 4 queues.

• Go serial first, and as you find performance bottle necks, measure why, and if concurrency helps, apply with care, always validating under system pressure. Reuse

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// Swift's untyped errors are a goddam PiTA. Here's the pattern I use to try to work around this.
// The goal is basically to try to guarantee that every throwing function in the app throws an
// ApplicationError instead of some unknown error type. We can't actually enforce this statically
// But by following this convention we can simplify error handling

enum ApplicationError: Error, CustomStringConvertible {
    
  // These are application-specific errors that may need special treatment
  case specificError1
  case specificError2(SomeType)

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extension Dictionary {
    mutating func value(for key: Key, orAdd closure: @autoclosure () -> Value) -> Value {
        if let value = self[key] {
            return value
        }
        
        let value = closure()
        self[key] = value
        return value
    }

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final class SampleViewController: StoryboardBackedViewController {
    // Unfortunately this must be an IUO var, so that we can set the value after super.init
    private var member: Foo!
    
    // Proper dependency injection in a storyboard backed VC!
    init(foo: Foo) {
        super.init(storyboardIdentifier: "SampleViewControllerIdentifier")

        // We have to set the members *after* calling super.init, since it changes the instance of `self`.
        self.member = foo

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Studying for a Tech Interview Sucks, so Here's a Cheat Sheet to Help

This list is meant to be a both a quick guide and reference for further research into these topics. It's basically a summary of that comp sci course you never took or forgot about, so there's no way it can cover everything in depth. It also will be available as a gist on Github for everyone to edit and add to.

Data Structure Basics

###Array ####Definition:

• Stores data elements based on an sequential, most commonly 0 based, index.
• Based on tuples from set theory.

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// gem install cocoapods-playgrounds
// pod playgrounds LibYAML

// Update: @floriankugler had a great idea to use UnsafeBufferPointer

// Paste in the following:

import LibYAML

public struct YAMLError: ErrorType {

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Better Unwrapping

• Proposal: TBD
• Author: Erica Sadun, Chris Lattner, Xiaodi Wu David Goodine
• Status: TBD
• Review manager: TBD

Introduction

This proposal redesigns common unwrapping tasks:

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Apps to install from macOS App Store:

• Tweetbot
• CopyClip 2
• GIF Brewery
• Slack
• Deckset
• Keynote/Pages/Numbers
• 1Password
• OmniFocus 2

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struct Coordinator {
  let window: UIWindow
  let navCtrl: UINavigationController?
  
  func start() {
    presentWelcomeScreen()
  }
  
  private func presentWelcomeScreen() {
    let vc = WelcomeScreenViewController() // Instanciate from code, XIB, Storyboard, whatever your jam is

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#!/usr/bin/env xcrun swift -F Carthage/Build/Mac

import Foundation
import Markingbird

protocol Streamable {
    var title: String { get }
    var body: String { get }
}