Xinghua flexih

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].

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 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

	// https://www.cs.rit.edu/~ncs/color/t_convert.html
	struct RGB {
	// Percent
	let r: Float // [0,1]
	let g: Float // [0,1]
	let b: Float // [0,1]

	static func hsv(r: Float, g: Float, b: Float) -> HSV {
	let min = r < g ? (r < b ? r : b) : (g < b ? g : b)
	let max = r > g ? (r > b ? r : b) : (g > b ? g : b)

	# The trick is to link the DeviceSupport folder from the beta to the stable version.
	# sudo needed if you run the Mac App Store version. Always download the dmg instead... you'll thank me later :)

	# Support iOS 15 devices (Xcode 13.0) with Xcode 12.5:
	sudo ln -s /Applications/Xcode-beta.app/Contents/Developer/Platforms/iPhoneOS.platform/DeviceSupport/15.0 /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/DeviceSupport

	# Then restart Xcode and reconnect your devices. You will need to do that for every beta of future iOS versions

	# (A similar approach works for older versions too, just change the version number after DeviceSupport)

	//: # Glucose Value Conversion on iOS 10.

	import Foundation // iOS 10.0, wathOS 3.0, macOS 10.12


	/*:
	****
	## Current Nightscouter Implmentation

	- Note: The current app treats glucose values as an aliased Double.

	import UIKit

	@UIApplicationMain
	class AppDelegate: UIResponder, UIApplicationDelegate {

	var window: UIWindow?

	func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {

	let window = UIWindow(frame: UIScreen.main.bounds)

	extern void SACLockScreenImmediate ( );

	SACLockScreenImmediate();

	import Foundation
	import UIKit

	struct ViewStyle<T> {
	let style: (T) -> Void
	}

	let filled = ViewStyle<UIButton> {
	$0.setTitleColor(.white, for: .normal)
	$0.backgroundColor = .red

	//
	// UIView+Tooltips.h
	// Crossword
	//
	// Created by Steven Troughton-Smith on 13/09/2019.
	// Copyright © 2019 Steven Troughton-Smith. All rights reserved.
	//

	#import <UIKit/UIKit.h>