Diogo Tridapalli diogot

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,

Using private Objective-C classes from Swift

In Objective-C, if you want to make use of one of Apple's internal classes, all you have to do is declare the class's interface with the methods you want to use. From there you can create instances of the class by using the NSClassFromString function to obtain a reference to the class object, like so:

[[NSClassFromString(@"_NSSomeClass") alloc] initWithFoo:5]

In Swift, this is not so easy. Referencing the type of the "hollow" Objective-C class interface anywhere in Swift code makes the compiler query the class for type information that is not known at compile time. This presents a huge problem. You cannot dynamically initialize a type either. Though, it seems the following code used to work at one point:

Hacking UIView animation blocks for fun and profit

In this article, I'm going to explore a way that we can create views that implement custom Core Animation property animations in a natural way.

As we know, layers in iOS come in two flavours: Backing layers and hosted layers. The only difference between them is that the view acts as the layer delegate for its backing layer, but not for any hosted sublayers.

In order to implement the UIView transactional animation blocks, UIView disables all animations by default and then re-enables them individually as required. It does this using the actionForLayer:forKey: method.

Somewhat strangely, UIView doesn't enable animations for every property that CALayer does by default. A notable example is the layer.contents property, which is animatable by default for a hosted layer, but cannot be animated using a UIView animation block.

	#import <Foundation/Foundation.h>
	#import <CoreData/CoreData.h>

	@class MHWMigrationManager;

	@protocol MHWMigrationManagerDelegate <NSObject>

	NS_ASSUME_NONNULL_BEGIN
	@optional
	- (void)migrationManager:(MHWMigrationManager *)migrationManager migrationProgress:(float)migrationProgress;

	struct Video {

	let title: String
	let description: String?
	let category: String
	let thumbnailUrl: URL?
	let …

	}

	import Foundation

	enum CardTypeError:Error {
	case TypeNotFound
	}

	enum CardType:CustomStringConvertible {
	case visa
	case mastercard
	case amex

	NSDate *date = [NSDate new];

	NSDateFormatter *dateFormatter = [NSDateFormatter new];
	dateFormatter.locale = [NSLocale localeWithLocaleIdentifier:@"nl_NL"];
	dateFormatter.dateStyle = NSDateFormatterFullStyle;
	dateFormatter.formattingContext = NSFormattingContextDynamic; // this is the important setting

	NSString *dateString = [dateFormatter stringFromDate:date];

	NSString *s1 = [NSString stringWithFormat:@"Foo %@", dateString]; // "Foo dinsdag 13 december 2016"

	# 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)

	class PersonBuilder {

	private final var name: String
	private final var age: String?
	private final var gender: String?

	init(name: String) {
	self.name = name
	}

	import UIKit

	struct Screen<A> {
	let run: (A -> ()) -> UIViewController
	}

	struct Step<A> {
	let build: (navigationController: UINavigationController, callback: A -> ()) -> UIViewController
	}