Slava svyatoslav-zubrin

1. The Layer Tree

Core Animation's original name is Layer Kit

Core Animation is a compositing engine; its job is to compose different pieces of visual content on the screen, and to do so as fast as possible. The content in question is divided into individual layers stored in a hierarchy known as the layer tree. This tree forms the underpinning for all of UIKit, and for everything that you see on the screen in an iOS application.

In UIView, tasks such as rendering, layout and animation are all managed by a Core Animation class called CALayer. The only major feature of UIView that isn’t handled by CALayer is user interaction.

There are four hierarchies, each performing a different role:

Install a new Ruby with rbenv on Mac OS (and make yourself a superhero)

If you're doing stuff with Ruby on a Mac, e.g. installling Jekyll or something, by default you'll end up having to use the sudo command to do stuff, since the permission to modify the default config is not available to your user account.

This sucks and should be avoided. Here's how to fix that.

Installing a new Ruby

To make this better, we are going install a new, custom Ruby. This used to be a big, scary thing, but thanks to the awesome tools Homebrew and rbenv, it's a snap.*

A word of warning: you will have to use Terminal to install this stuff. If you are uncomfortable with text, words, and doing stuff with your computer beyond pointing and hoping, this may not work well for you. But if that's the case, I'm not sure why you were trying to use Ruby in the first place.

	// The MIT License (MIT)
	//
	// Copyright (c) 2017 Alexander Grebenyuk (github.com/kean).

	import Foundation
	import RxSwift
	import RxCocoa


	extension ObservableType {

	import RxSwift // Version 3.2.0
	import RxCocoa // Version 3.2.0

	func keyboardHeight() -> Observable<CGFloat> {
	return Observable
	.from([
	NotificationCenter.default.rx.notification(NSNotification.Name.UIKeyboardWillShow)
	.map { notification -> CGFloat in
	(notification.userInfo?[UIKeyboardFrameBeginUserInfoKey] as? NSValue)?.cgRectValue.height ?? 0
	},

	// Created by Vasily Ulianov on 09.02.17, updated in 2019.
	// License: MIT

	import Foundation

	/// Subclass of `Operation` that adds support of asynchronous operations.
	/// 1. Call `super.main()` when override `main` method.
	/// 2. When operation is finished or cancelled set `state = .finished` or `finish()`
	open class AsynchronousOperation: Operation {
	public override var isAsynchronous: Bool {

	//: [Previous](@previous)

	import Foundation

	// One per function
	final class Stub {
	let name: String
	let cmp: (AnyCall, AnyCall) -> Bool
	init(name: String, cmp: (AnyCall, AnyCall) -> Bool) {
	self.name = name

	//: Playground - noun: a place where people can play

	protocol Cat {
	func meow() -> String
	}

	protocol Dog {
	func bark() -> String
	}