Witold Skibniewski mr-v

If you work on a Swift project that follows the Model-View-ViewModel (MVVM) architecture or similar, you may want to jump to counterpart in Xcode from your view to your model, and then to your view model. (ie. by using Ctrl+Cmd+Up and Ctrl+Cmd+Down).

You can do this in recent versions of Xcode by setting a configuration default.

From a terminal, just type this command and press Enter:

defaults write com.apple.dt.Xcode IDEAdditionalCounterpartSuffixes -array-add "ViewModel" "View"

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

legacy = UIGraphicsBeginImageContextWithOptions + UIGraphicsEndImageContext

modern = UIGraphicsImageRendererFormat + UIGraphicsImageRenderer

Take aways:

"modern" w/ prefersExtendedRange = NO
- basically the same perf as "legacy"
- probably a good idea to adopt since optimizations will likely be in "modern" first
"modern" w/ prefersExtendedRange = YES

DEPRECATED for Xcode 10 🎈

(check out What's New in Swift at 11:40, slide 42)

Whole Module Compilation Optimizations: Why these terms are sometimes misleading

When you look up how to compile swift faster for debug builds, people very earnestly give advice that seems contradictory: you should "try using the whole module optimization flag," and also "never use whole module optimization for debugging". [^1]

This is confusing because some of us are using these two general words:

compilation: "turning text into an executable program"

Logic composability problems of lifecycle hooks in React

Suppose I have these components in my project:

class MessageHeader extends React.Component { /* ... */ }

class NiceButton extends React.Component { /* ... */ }

class FridgeContents extends React.Component { /* ... */ }

	import UIKit

	#if canImport(SwiftUI) && DEBUG
	import SwiftUI
	struct UIViewControllerPreview<ViewController: UIViewController>: UIViewControllerRepresentable {
	let viewController: ViewController

	init(_ builder: @escaping () -> ViewController) {
	viewController = builder()
	}

	// Douglas Hill, December 2018
	// Made for https://douglashill.co/reading-app/
	// Find the latest version of this file at https://github.com/douglashill/KeyboardKit

	import UIKit

	/// A table view that allows navigation and selection using a hardware keyboard.
	/// Only supports a single section.
	class KeyboardTableView: UITableView {
	// These properties may be set or overridden to provide discoverability titles for key commands.

	import Darwin

	@dynamicMemberLookup
	struct Environment {
	subscript(dynamicMember name: String) -> String? {
	get {
	guard let value = getenv(name) else { return nil }

	return String(validatingUTF8: value)
	}

	https://statici.icloud.com/fmipmobile/deviceImages-9.0/iPhone/iPhone9,4-2-3-0/online-infobox__3x.png
	A B C D E F G

	A: deviceImages version seems to determine the format of the image specifier (C, D, E, F)
	B: device marketing name
	C: device model identifier
	D: color cover glass (front color)
	1 - Black
	2 - White
	E: device enclosure color (back color)