new vs alloc init

概述在object-c基础教程这本书里老是可以看见类似下面这种代码，我这小菜鸟就纳闷了，啥区别啊，看上去都一样么。网上找了找，找到一些说法，这里先摘出来。 someClass* object = [someClass new]; or someClass* object = [[someClass alloc] init]; 其实是一样的，某位老兄是这样说的，new在内部调用的alloc和init, 在object-c基础教程这本书里老是可以看见类似下面这种代码，我这小菜鸟就纳闷了，啥区别啊，看上去都一样么。网上找了找，找到一些说法，这里先摘出来。
someClass* object = [someClass new];
or
someClass* object = [[someClass alloc] init];

其实是一样的，某位老兄是这样说的，new在内部调用的alloc和init,
Actually "new" is not a keyword in Objective-C,but NSObject implements a class method "new" which simply calls "alloc" and "init".

既然一样干嘛有两个，吃饱了那个啥来着。。
The new method actually comes from NeXT days. Back then,there was no two phase initialization,it was just a single new method. They soon realized that a two phase approach Could have advantages,and introduced alloc. new was kinda deprecated,but kept in for backwards compatibility. It is exactly the same as alloc-init. Use 'new' if it suits. One shortcoming is that it only works with the basic 'init' initializer,and will not work with other initializers (eg initWithString:).
背景说明，new是较为老式的写法，后来发现只有一个new不好使，才引入了alloc和init这种写法，保留new一是向后兼容，二是很多时候是一种更简单的写法。至于alloc这种写法可以变出这样的花来，

Frequently,you are going to need to pass arguments to init and so you will be using a different method,such as [[SomeObject alloc] initWithString: @"Foo"]. If you're used to writing this,you get in the habit of doing it this way and so [[SomeObject alloc] init] may come more naturally that [SomeObject new].
恩，确实如果不需要用其他的init函数，比如initWithString,用new的方法，毫无疑问是更加方便的。

再来个据说是来源比较靠谱的说法：
There was a very long thread on this same subject (alloc/init vs. new) on the cocoa-dev mailing List this week (search for "[Foo new] vs [[Foo alloc] init]"). Unfortunately the documentation is not crystal clear on this,but Bill Bumgarner (an Apple Engineer) confirmed that new is implemented as allocWithZone/alloc followed by init back at least to the beginning of OS X. So the answer is,use whichever you prefer. The current vogue in Cocoa programming is to use alloc/init because it makes the intended behavior explicit.
好吧，似乎只有显示调用更加容易理解这一个区别了，总之一句话，爱谁谁。

这位兄弟来了个总结性发言，姑且咱先信了他，
* new doesn't support custom initializers (like initWithString)
* alloc-init is more explicit than new
General opinion seems to be that you should use whatever you're comfortable with.

以上的说法都来自http://macresearch.org/difference-between-alloc-init-and-new,有兴趣的看看把。

From: http://www.cnblogs.com/ulihj/archive/2011/01/15/1936342.HTML

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