A simple Singleton template in Objective-C, based on the Big Nerd Ranch snippet

Singleton.m

///
/// A singleton class template for header (.h)
///
@interface Singleton : NSObject

+ (Singleton*)shared;

@end

///
/// A singleton class template for code file (.m)
///
@implementation Settings

#pragma mark - Singleton Implementation 

///
/// Gets the singleton instance of this class
///
+ (Singleton *)shared
{
    static Singleton *instance = nil;
    if(!instance)
        instance = [[super allocWithZone:nil] init];
    return instance;
}

///
/// Override the base alloc to ensure we're always returning the same object
///
+ (id)allocWithZone:(NSZone *)zone
{
    return [self shared];
}

@end