Data commit

Task/Singleton/Objective-C/singleton-1.m

@@ -0,0 +1,9 @@
+// SomeSingleton.h
+@interface SomeSingleton : NSObject
+{
+  // any instance variables
+}
+
++ (SomeSingleton *)sharedInstance;
+
+@end

Task/Singleton/Objective-C/singleton-2.m

@@ -0,0 +1,38 @@
+// SomeSingleton.m
+@implementation SomeSingleton
+
++ (SomeSingleton *) sharedInstance
+{
+   static SomeSingleton *sharedInstance = nil;
+   if (!sharedInstance) {
+      sharedInstance = [[SomeSingleton alloc] init];
+   }
+   return sharedInstance;
+}
+
+- (id)copyWithZone:(NSZone *)zone
+{
+    return self;
+}
+
+- (id)retain
+{
+    return self;
+}
+
+- (unsigned)retainCount
+{
+    return UINT_MAX;
+}
+
+- (oneway void)release
+{
+    // prevent release
+}
+
+- (id)autorelease
+{
+    return self;
+}
+
+@end

Task/Singleton/Objective-C/singleton-3.m

@@ -0,0 +1,10 @@
++ (SomeSingleton *) sharedInstance
+{
+   static SomeSingleton *sharedInstance = nil;
+   @synchronized(self) {
+      if (!sharedInstance) {
+         sharedInstance = [[SomeSingleton alloc] init];
+      }
+   }
+   return sharedInstance;
+}

Task/Singleton/Objective-C/singleton-4.m

@@ -0,0 +1,9 @@
++ (SomeSingleton *) sharedInstance
+{
+   static SomeSingleton *sharedInstance = nil;
+   static dispatch_once_t onceToken;
+   dispatch_once(&onceToken, ^{
+      sharedInstance = [[SomeSingleton alloc] init];
+   });
+   return sharedInstance;
+}