Baoshan Sheng baoshan

What is the Strict Aliasing Rule and Why do we care?

(OR Type Punning, Undefined Behavior and Alignment, Oh My!)

What is strict aliasing? First we will describe what is aliasing and then we can learn what being strict about it means.

In C and C++ aliasing has to do with what expression types we are allowed to access stored values through. In both C and C++ the standard specifies which expression types are allowed to alias which types. The compiler and optimizer are allowed to assume we follow the aliasing rules strictly, hence the term strict aliasing rule. If we attempt to access a value using a type not allowed it is classified as undefined behavior(UB). Once we have undefined behavior all bets are off, the results of our program are no longer reliable.

Unfortunately with strict aliasing violations, we will often obtain the results we expect, leaving the possibility the a future version of a compiler with a new optimization will break code we th

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,

OS X Screencast to animated GIF

This gist shows how to create a GIF screencast using only free OS X tools: QuickTime, ffmpeg, and gifsicle.

Instructions

To capture the video (filesize: 19MB), using the free "QuickTime Player" application:

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-// Example: https://codepen.io/marcelo-ribeiro/pen/OJmVOyW
-const accentsMap = new Map([
-  ["A", "Á|À|Ã|Â|Ä"],
-  ["a", "á|à|ã|â|ä"],
-  ["E", "É|È|Ê|Ë"],
-  ["e", "é|è|ê|ë"],
-  ["I", "Í|Ì|Î|Ï"],
-  ["i", "í|ì|î|ï"],
-  ["O", "Ó|Ò|Ô|Õ|Ö"],

	#include <cassert>
	#include <cstdlib>
	#include <iostream>

	#include <AudioUnit/AudioUnit.h>
	#include <CoreAudio/CoreAudio.h>

	#define kAudioUnitOutputBus 0
	#define kAudioUnitInputBus 1

	//
	// ToneOutputUnit.swift
	//
	// This is a Swift 3 class (which should be instantiated as a singleton object)
	// that can play a single tone of arbitrary tone and frequency on iOS devices
	// using run-time sinewave synthesis and the Audio Unit v3 API with RemoteIO.
	//
	// Created by Ronald Nicholson rhn@nicholson.com on 2/20/2016.
	// revised 2016-Sep-08 for Swift 3
	// http://www.nicholson.com/rhn/

	#import <Foundation/Foundation.h>

	typedef void(^AsyncBlock)(dispatch_block_t completionHandler);

	@interface AsyncBlockOperation : NSOperation

	@property (nonatomic, readonly, copy) AsyncBlock block;

	+ (instancetype)asyncBlockOperationWithBlock:(AsyncBlock)block;

	//
	// ViewController.m
	// AVPlayerCaching
	//
	// Created by Anurag Mishra on 5/19/14.
	// Sample code to demonstrate how to cache a remote audio file while streaming it with AVPlayer
	//

	#import "ViewController.h"
	#import <AVFoundation/AVFoundation.h>

	var editor = new CodeMirror({ /* ... */ });

	fake(editor, "("); // if you have closebrackets.js addon switched on, this will actually generate "()"
	fake(editor, "enter"); // all the crazy indenting logic will be used
	fake(editor, "e"); // just letter "e"
	fake(editor, 48); // 0
	fake(editor, "leftArrow", ["ctrlKey", "shiftKey"]);