Nutchaphon Rewik nRewik

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

This document has moved!

It's now here, in The Programmer's Compendium. The content is the same as before, but being part of the compendium means that it's actively maintained.

A composable pattern for pure state machines with effects

State machines are everywhere in interactive systems, but they're rarely defined clearly and explicitly. Given some big blob of code including implicit state machines, which transitions are possible and under what conditions? What effects take place on what transitions?

There are existing design patterns for state machines, but all the patterns I've seen complect side effects with the structure of the state machine itself. Instances of these patterns are difficult to test without mocking, and they end up with more dependencies. Worse, the classic patterns compose poorly: hierarchical state machines are typically not straightforward extensions. The functional programming world has solutions, but they don't transpose neatly enough to be broadly usable in mainstream languages.

Here I present a composable pattern for pure state machiness with effects,

###Redux Egghead Video Notes###

####Introduction:#### Managing state in an application is critical, and is often done haphazardly. Redux provides a state container for JavaScript applications that will help your applications behave consistently.

Redux is an evolution of the ideas presented by Facebook's Flux, avoiding the complexity found in Flux by looking to how applications are built with the Elm language.

####1st principle of Redux:#### Everything that changes in your application including the data and ui options is contained in a single object called the state tree

Here's my own list of the interesting stuff announced during this year's WWDC, collected from the keynotes, various Apple docs, blog posts and tweets.

If you're planning to watch the videos, I really recommend this Mac app that helps you download and watch them: https://github.com/insidegui/WWDC.

OS X El Capitan

http://www.apple.com/osx/elcapitan-preview/

split view - two apps side by side on full screen

	import UIKit

	class ViewController: UIViewController, UITableViewDelegate, UITableViewDataSource {

	@IBOutlet weak var tableView: UITableView!

	override func viewDidLoad() {
	super.viewDidLoad()
	NSLayoutConstraint.activate([
	tableView.topAnchor.constraint(equalTo: view.topAnchor),

	// paste in your console
	speechSynthesis.onvoiceschanged = function() {
	var msg = new SpeechSynthesisUtterance();
	msg.voice = this.getVoices().filter(v => v.name == 'Cellos')[0];
	msg.text = Object.keys(window).join(' ');
	this.speak(msg);
	};

	// Variables just contain an integer. We can have a maximum of `Int.max` variables in our program. ¯\_(ツ)_/¯

	private struct Var {
	static var freshVarIx = 0
	let ix: Int
	init() {
	Var.freshVarIx+=1
	ix = Var.freshVarIx
	}
	}

	//
	// UIImage+Orientation.swift
	// DrCloudPatient
	//
	// Created by DW78 on 8/21/15.
	// Copyright (c) 2015 DW78. All rights reserved.
	//

	import UIKit