장석순(Jang Seoksoon) boraseoksoon

Reliable mouseEnter/Exit for SwiftUI

On Mac, SwiftUI's .onHover closure is not always called on mouse exit, particularly with high cursor velocity. A grid of targets or with finer target shapes will often have multiple targets falsely active after the mouse has moved on.

It is easy to run back to AppKit's safety. Below is a SwiftUI-like modifier for reliable mouse-tracking. You can easily adapt it for other mouse tracking needs.

import SwiftUI

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 a small demo of how to create a library in Rust and call it from Python (both CPython and PyPy) using the CFFI instead of ctypes.

Based on http://harkablog.com/calling-rust-from-c-and-python.html (dead) which used ctypes

CFFI is nice because:

Reads C declarations (parses headers)
Works in both CPython and PyPy (included with PyPy)
Lower call overhead than ctypes

Build Your Own LISP

I had fun building my own LISP (Slow Loris). The project was extremely easy to get off the ground, because there a ton of resources to do just this. I thought it might be handy to have a little links round-up, based on my research.

In Python

There are already several good projects out there on writing your own LISP in Python.

Peter Norvig's LisPy

Pure for guarantied value semantics

Author: Michel Fortin

Introduction

This proposal introduces the concept of pure functions to Swift. A pure function is guarantied to allow only value semantics, even when dealing with classes.

	#import <Carbon/Carbon.h>
	#import <dlfcn.h>

	/*
	* Returns an array of CFDictionaryRef types, each of which contains information about one of the processes.
	* The processes are ordered in front to back, i.e. in the same order they appear when typing command + tab, from left to right.
	* See the ProcessInformationCopyDictionary function documentation for the keys used in the dictionaries.
	* If something goes wrong, then this function returns NULL.
	*/
	CFArrayRef CopyLaunchedApplicationsInFrontToBackOrder(void)

	//
	// debounce-throttle.swift
	//
	// Created by Simon Ljungberg on 19/12/16.
	// License: MIT
	//

	import Foundation

	extension TimeInterval {

	extension Collection {
	func parallelMap<T>(
	parallelism requestedParallelism: Int? = nil,
	_ transform: @escaping (Element) async throws -> T
	) async throws -> [T] {
	let defaultParallelism = 2
	let parallelism = requestedParallelism ?? defaultParallelism

	let n = self.count
	if n == 0 {

	// See commentary below this gist.
	import Foundation
	import QuartzCore

	// Implementation from https://talk.objc.io/episodes/S01E90-concurrent-map
	public final class ThreadSafe<A> {
	var _value: A
	let queue = DispatchQueue(label: "ThreadSafe")
	init(_ value: A) { self._value = value }

	import UIKit

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

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