Editing Closure (computer programming) (section)

=== Blocks (C, C++, Objective-C 2.0) ===
{{Main|Blocks (C language extension)}}
[[Apple Inc.|Apple]] introduced [[Blocks (C language extension)|blocks]], a form of closure, as a nonstandard extension into [[C (programming language)|C]], [[C++]], [[Objective-C 2.0]] and in [[Mac OS X Snow Leopard|Mac OS X 10.6 "Snow Leopard"]] and [[iOS 4]].0. Apple made their implementation available for the GCC and clang compilers.

Pointers to block and block literals are marked with <code>^</code>. Normal local variables are captured by value when the block is created, and are read-only inside the block. Variables to be captured by reference are marked with <code>__block</code>. Blocks that need to persist outside of the scope they are created in may need to be copied.<ref>{{cite web |url=https://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/Blocks/Articles/00_Introduction.html |title=Blocks Programming Topics |author=<!-- Unstated staff writer --> |date=8 March 2011 |publisher=Apple Inc. |access-date=2011-03-08}}</ref><ref>{{cite web |url=http://thirdcog.eu/pwcblocks/ |title=Programming with C Blocks on Apple Devices |last=Bengtsson |first=Joachim |date=7 July 2010|access-date=2010-09-18|archive-url=https://web.archive.org/web/20101025034928/http://thirdcog.eu/pwcblocks/|archive-date=25 October 2010|url-status=dead}}</ref>

<syntaxhighlight lang="objc">
typedef int (^IntBlock)();

IntBlock downCounter(int start) {
	 __block int i = start;
	 return [[ ^int() {
		 return i--;
	 } copy] autorelease];
}

IntBlock f = downCounter(5);
NSLog(@"%d", f());
NSLog(@"%d", f());
NSLog(@"%d", f());
</syntaxhighlight>