This is a singleton class for iOS, Objective-C, Cocoa Touch, iPhone, iPad.

KLSingleton is:

1. Subclassible (to the n-th degree)
2. ARC compatible
3. Safe with alloc and init
4. Thread-safe
5. Lock-free (uses +initialize, not @synchronize)
6. Macro-free
7. Swizzle-free
8. Simple

This implementation chooses the singleton philosophy of "not lazy" instead of "requires explicit initialization" or "locks to allocate".

1. Add the files to your project
2. Import the header using #import "KLSingleton.h"
3. Subclass the KLSingleton class in the following way:

@interface MYSubclass : KLSingleton

You may then retrieve the unique, ready-to-use instance of your class by calling any of the following methods:

[MYSubclass instance]
[MYSubclass sharedInstance] //alias
[MYSubclass singleton]      //alias
[[MYSubclass alloc] init]   //bad style, but safe to call any number of times

If you need to lazily allocate a large instance variable use dispatch_once in the getter. You might do this if, for instance, you needed 500MB of workspace but did not want that memory to be allocated on startup.

1. This has been tested on ARC only. Test on projects without ARC support.
2. See if there are any meaningful differences with the swizzle method.
3. Macro the options to become lazy and either "require initialization" or "lock to allocate"
4. Something like dispatch_once that ran once for each subclass would let us be lazy for free. Per-subclass tokens?

Released under ISC (similar to 2-clause BSD)