singleton pattern in cocoa
Hi all,
As I come from java world, I was trying to implement the singleton
pattern, very usual in java. After searching in internet I found this
code from wikipedia:
@interface MySingleton : NSObject
{
}
+ (MySingleton *)sharedSingleton;
@end
@implementation MySingleton
static MySingleton *sharedSingleton;
+ (MySingleton *)sharedSingleton
{
@synchronized(self)
{
if (!sharedSingleton)
[[MySingleton alloc] init];
return sharedSingleton;
}
}
+(id)alloc
{
@synchronized(self)
{
NSAssert(sharedSingleton == nil, @"Attempted to allocate a second
instance of a singleton.");
sharedSingleton = [super alloc];
return sharedSingleton;
}
}
@end
What do you think about this implementation? I'm newbie with cocoa and
I'm not sure.
Thanks.
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Re: singleton pattern in cocoa
This question usually gets asked at least a couple times a month. I
suggest you look up the previous responses on CocoaBuilder (http://www.cocoabuilder.com/
), which archives responses on this mailing list if you want an
exhaustive response, since all solutions have been mentioned somewhere
here before.
- Bryan
On Sep 10, 2009, at 4:07:36 PM, Manuel Grau wrote:
Hi all,
As I come from java world, I was trying to implement the singleton
pattern, very usual in java. After searching in internet I found
this code from wikipedia:
@interface MySingleton : NSObject
{
}
+ (MySingleton *)sharedSingleton;
@end
@implementation MySingleton
static MySingleton *sharedSingleton;
+ (MySingleton *)sharedSingleton
{
@synchronized(self)
{
if (!sharedSingleton)
[[MySingleton alloc] init];
return sharedSingleton;
}
}
+(id)alloc
{
@synchronized(self)
{
NSAssert(sharedSingleton == nil, @"Attempted to allocate a second
instance of a singleton.");
sharedSingleton = [super alloc];
return sharedSingleton;
}
}
@end
What do you think about this implementation? I'm newbie with cocoa
and I'm not sure.
Thanks.
___
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Re: singleton pattern in cocoa
Singleton implementation is something that you see debated back and forth every now and then. People argue about the values over overriding -retain, -release, -autorelease, and so on. I really like Peter Hosey's analysis (and implementation) that he's posted on his blog: http://boredzo.org/blog/archives/2009-06-17/doing-it-wrong Cheers, Dave On Sep 10, 2009, at 2:07 PM, Manuel Grau wrote: Hi all, As I come from java world, I was trying to implement the singleton pattern, very usual in java... ___ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
Re: singleton pattern in cocoa
About the only thing that I'd recommend is that the "static" be inside
the +sharedSingleton method so that you aren't able to take the cheap-
way-out and call that variable directly in other class methods before
it's created.
For the rest of it: it seems to follow Apple's patterns - for
instance, [NSNotificationCenter defaultCenter] and [NSStatusBar
systemStatusBar] and [UIAccelerometer sharedAccelerometer] and
sharedAddressBook... etc
A lot of things use the sharedMyClass, but a lot (though fewer) of
things also use their own name.
That method of singletons is pretty common though.
On 10 Sep 2009, at 1:07 PM, Manuel Grau wrote:
Hi all,
As I come from java world, I was trying to implement the singleton
pattern, very usual in java. After searching in internet I found
this code from wikipedia:
@interface MySingleton : NSObject
{
}
+ (MySingleton *)sharedSingleton;
@end
@implementation MySingleton
static MySingleton *sharedSingleton;
+ (MySingleton *)sharedSingleton
{
@synchronized(self)
{
if (!sharedSingleton)
[[MySingleton alloc] init];
return sharedSingleton;
}
}
+(id)alloc
{
@synchronized(self)
{
NSAssert(sharedSingleton == nil, @"Attempted to allocate a second
instance of a singleton.");
sharedSingleton = [super alloc];
return sharedSingleton;
}
}
@end
What do you think about this implementation? I'm newbie with cocoa
and I'm not sure.
Thanks.
___
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Re: singleton pattern in cocoa
Definition of true singleton is generally discouraged and not really
useful.
See more info about it here:
http://eschatologist.net/blog/?p=178
Le 10 sept. 2009 à 22:07, Manuel Grau a écrit :
Hi all,
As I come from java world, I was trying to implement the singleton
pattern, very usual in java. After searching in internet I found
this code from wikipedia:
@interface MySingleton : NSObject
{
}
+ (MySingleton *)sharedSingleton;
@end
@implementation MySingleton
static MySingleton *sharedSingleton;
+ (MySingleton *)sharedSingleton
{
@synchronized(self)
{
if (!sharedSingleton)
[[MySingleton alloc] init];
return sharedSingleton;
}
}
+(id)alloc
{
@synchronized(self)
{
NSAssert(sharedSingleton == nil, @"Attempted to allocate a second
instance of a singleton.");
sharedSingleton = [super alloc];
return sharedSingleton;
}
}
@end
What do you think about this implementation? I'm newbie with cocoa
and I'm not sure.
Thanks.
___
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-- Jean-Daniel
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Re: singleton pattern in cocoa
Probably best to use Apple's example:
http://developer.apple.com/mac/library/documentation/Cocoa/Conceptual/CocoaFundamentals/CocoaObjects/CocoaObjects.html#//apple_ref/doc/uid/TP40002974-CH4-SW32
I love Google, but I always prefer to look at Apple's docs first. I
found the above by going to developer.apple.com and typing in
"Singleton" in the search field.
On Sep 10, 2009, at 3:07 PM, Manuel Grau wrote:
Hi all,
As I come from java world, I was trying to implement the singleton
pattern, very usual in java. After searching in internet I found
this code from wikipedia:
@interface MySingleton : NSObject
{
}
+ (MySingleton *)sharedSingleton;
@end
@implementation MySingleton
static MySingleton *sharedSingleton;
+ (MySingleton *)sharedSingleton
{
@synchronized(self)
{
if (!sharedSingleton)
[[MySingleton alloc] init];
return sharedSingleton;
}
}
+(id)alloc
{
@synchronized(self)
{
NSAssert(sharedSingleton == nil, @"Attempted to allocate a second
instance of a singleton.");
sharedSingleton = [super alloc];
return sharedSingleton;
}
}
@end
What do you think about this implementation? I'm newbie with cocoa
and I'm not sure.
Thanks.
___
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