Max Sokolov maxsokolov

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,

Greetings and salutations, NSHipsters!

As the year winds down, it's a tradition here at NSHipster to ask you, dear readers, to offer up your favorite tricks and tips from the past year as gifts to your fellow hipsters. With iOS 9, El Capitan, brand new watch- and tvOS's, and the open-sourcing of some minor Apple-related tech, there's bound to be lots to share.

Submit your favorite piece of Swift or @objc trivia, helpful hints, unexpected discoveries, useful workarounds, useless fascinations, or anything else you found cool this year. Just comment below!

If you need inspiration, try [the list from last year][2015], or [from the year before][2014], or [from the year before that][2013].

	import UIKit
	import Foundation

	func test(named: String,
	_ work: (_ assert: @escaping (Bool) -> Void, _ done: @escaping () -> Void) -> Void) {
	var testPass = true
	var assertCount = 0
	let assert: (Bool) -> Void = { value in
	assertCount = assertCount + 1
	testPass = testPass && value

	@objc protocol Refreshable
	{
	/// The refresh control
	var refreshControl: UIRefreshControl? { get set }

	/// The table view
	var tableView: UITableView! { get set }

	/// the function to call when the user pulls down to refresh
	@objc func handleRefresh(_ sender: Any);

	// The issue with sectionHeadersPinToVisibleBounds and sectionFootersPinToVisibleBounds is that they do not pin
	// first header and last footer when bouncing. This layout subclass fixes that.

	class StickyLayout: UICollectionViewFlowLayout {

	override init() {
	super.init()
	self.sectionFootersPinToVisibleBounds = true
	self.sectionHeadersPinToVisibleBounds = true
	}


	class Number /* class cluser */ {
	class Int8: Number {
	var value: Swift.Int8
	init(_ value: Swift.Int8) { self.value = value }
	}
	class Int: Number {
	var value: Swift.Int
	init(_ value: Swift.Int) { self.value = value }
	}

	function argsList(method) {
	method = method.toString();
	const fn = /^function\s[^\(]\(\s([^\)])\)/m;
	const cls = /constructor\s[^\(]\(\s([^\)])\)/m;
	const FN_ARGS = method[0] === 'f' ? fn : cls;
	const depsStr = method.match(FN_ARGS);
	const deps = (depsStr) ? depsStr[1].trim().split(/[\s,]+/) : [''];

	if (deps[0] === '') {
	return [];

	protocol AssetLoadable {

	var rawValue: String { get }
	func imageNamed() -> String
	}

	extension AssetLoadable {
	func imageNamed() -> String {
	return rawValue
	}

	/*
	* This is an example provided by Facebook are for non-commercial testing and
	* evaluation purposes only.
	*
	* Facebook reserves all rights not expressly granted.
	*
	* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
	* OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
	* FITNESS FOR A PARTICULAR PURPOSE AND NON INFRINGEMENT. IN NO EVENT SHALL
	* FACEBOOK BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN