Denis Lebedev delebedev

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

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:

Howdy howdy, NSHipsters!

If you alloc init an NSCalendar, you'll notice that New Year's Eve falls on a Monday this year, a.k.a. "the day NSHipster is published every week". What fun!

So in celebration of the upcoming year++, I thought it'd be fun to compile a list of some of your favorite tips and tricks of the trade. Submit your favorite piece of Objective-C trivia, framework arcana, hidden Xcode feature, or anything else you think is cool, and you could have it featured in the year-end blowout article. Just comment on this gist below!

Here are a few examples of the kind of things I'd like to see:

StaticObjcMethods from [Apple]((http://developer.apple.com/library/mac/#samplecode/CocoaTipsAndTricks/Introduction/Intro.html): Demonstrates how to use static Objective-C m

	As of iOS 11/macOS High Sierra, and only including ones in Foundation and CoreFoundation

	Strings:

	_NSCFString - a CFStringRef or CFMutableStringRef. This is the most common type of string object currently.
	- May have 8 bit (ASCII) or 16 bit (UTF-16) backing store
	_NSCFConstantString - a compile time constant CFStringRef, like you'd get with @"foo"
	- May also be generated by dynamic string creation if matches a string in a pre-baked table of common strings called the StringROM
	NSBigMutableString - an NSString backed by a CFStorage (https://github.com/opensource-apple/CF/blob/master/CFStorage.h) for faster handling of very large strings
	NSCheapMutableString - a very limited NSMutableString that allows for zero-copy initialization. Used in NSFileManager for temporarily wrapping stack buffers.

	extension Array {

	func first() -> Element? {
	if isEmpty {
	return nil
	}
	return self[0]
	}

	func last() -> Element? {

	// Taken from the commercial iOS PDF framework http://pspdfkit.com.
	// Copyright (c) 2014 Peter Steinberger, PSPDFKit GmbH. All rights reserved.
	// Licensed under MIT (http://opensource.org/licenses/MIT)
	//
	// You should only use this in debug builds. It doesn't use private API, but I wouldn't ship it.

	// PLEASE DUPE rdar://27192338 (https://openradar.appspot.com/27192338) if you would like to see this in UIKit.

	#import <objc/runtime.h>
	#import <objc/message.h>

	@implementation NSURLRequest (printCurlRequest)

	-(NSString *)curlRequest
	{
	__block NSString *curlstr = [NSString stringWithFormat:@"curl -k -X %@ --dump-header -",self.HTTPMethod];

	[[self allHTTPHeaderFields] enumerateKeysAndObjectsUsingBlock:^(id key, id obj, BOOL *stop) {
	curlstr = [curlstr stringByAppendingFormat:@" -H \"%@: %@\"",key, obj];
	}];

	// http://cocoawithlove.com/2009/10/ugly-side-of-blocks-explicit.html has a nice breakdown of the syntax--it helps to think of the ^ as similar to a pointer dereference symbol *

	// block typedef:

	typedef void(^Block)();
	typedef void(^ConditionalBlock)(BOOL);
	typedef NSString*(^BlockThatReturnsString)();
	typedef NSString*(^ConditionalBlockThatReturnsString)(BOOL);

	// block property with typedef:

	KEYWORDS="TODO:\|FIXME:\|\?\?\?:\|\!\!\!:"
	find "${SRCROOT}" \( -name ".h" -or -name ".m" \) -print0 \| xargs -0 egrep --with-filename --line-number --only-matching "($KEYWORDS).*\$" \| perl -p -e "s/($KEYWORDS)/ warning: \$1/"