Martin zeroelink

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

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,

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

	// Created by Matthew Johnson on 5/28/16.
	// Copyright © 2016 Anandabits LLC. All rights reserved.
	//
	// This is a minimalist implementation of a responder chain in pure Swift.
	//
	// It is not intended to demonstrate the best way to
	// implement event processing in Swift.
	//
	// The intent is to show how little code is necessary to acheive behavior
	// similar to Cocoa's responder chain in pure Swift.

	#!/bin/bash

	case $# in
	0)
	echo "Usage: $0 {start\|stop}"
	exit 1
	;;
	1)
	case $1 in
	start)

	import Foundation

	@objc protocol Foo {
	optional func say() -> String
	}

	class Doesnt: NSObject, Foo {
	}

	class Does: NSObject, Foo {

	/// Observes a run loop to detect any stalling or blocking that occurs.
	///
	/// This class is thread-safe.
	@interface GHRunLoopWatchdog : NSObject

	/// Initializes the receiver to watch the specified run loop, using a default
	/// stalling threshold.
	- (id)initWithRunLoop:(CFRunLoopRef)runLoop;

	/// Initializes the receiver to detect when the specified run loop blocks for

	import Prelude

	public struct Lens<A, B> {
	private let get: A -> B
	private let set: (A, B) -> A

	public init(get: A -> B, set: (A, B) -> A) {
	self.get = get
	self.set = set
	}

	struct Complex<T: FloatLiteralConvertible> {
	var real: T
	var imaginary: T
	}

	func +(lhs: Complex<Double>, rhs: Complex<Double>) -> Complex<Double> {
	return Complex<Double>(real: lhs.real + rhs.real, imaginary: lhs.imaginary + rhs.imaginary)
	}

	import Darwin

	extension Int {
	static func random() -> Int {
	return Int(arc4random())
	}

	static func random(range: Range<Int>) -> Int {
	return Int(arc4random_uniform(UInt32(range.endIndex - range.startIndex))) + range.startIndex
	}