使用ARC，生命周期限定符分配和unsafe_unretained [英] using ARC, lifetime qualifier assign and unsafe_unretained

问题描述

我对这两个限定符有点困惑...
使用ARC而不是使用弱（即如果我需要支持iOS 4）我可以使用 unsafe_unretained 丢失auto-nil功能......最终结果似乎类似于 assign 。

i'm a little confused about these two qualifiers... With ARC instead of using weak (i.e. if I need support iOS 4) I can use unsafe_unretained losing the auto-nil features... the final result seems to be similar to assign.

• 我可以用分配 unsafe_unretained >？


• 这些限定符是否相同？

• Can I exchange unsafe_unretained with assign ?
• Are these qualifiers the same thing ?

关于这个论点的Apple文档的任何链接都会非常有趣......我只能找到几行这里

It would be really interesting any link of Apple documentation on this argument... I can find only a few rows here

推荐答案

Clang的 ARC的技术规范详细介绍了限定符的工作原理。

Clang's technical specification of ARC goes into much more detail about how the qualifiers work.

但是，要回答你的问题： assign 和 __ unsafe_unretained 不是一回事。 assign 是一个属性属性，它告诉编译器如何合成属性的setter实现，而 __ unsafe_unretained 是一个所有权限定符，告诉ARC如何插入 retain / release 调用。但它们是相关的：在声明属性时， assign 暗示 __ unsafe_unretained 所有权。

But, to answer your question: assign and __unsafe_unretained are not the same thing. assign is a property attribute that tells the compiler how to synthesise the property's setter implementation, while __unsafe_unretained is an ownership qualifier that tells ARC how to insert retain/release calls. But they are related: when declaring a property, assign implies __unsafe_unretained ownership.

在ARC之前， assign 是默认的属性所有权限定符;但启用ARC后，可保留对象指针类型的默认值为 strong 。 （对于标量和其他指针类型， assign 仍然是默认值。）

Prior to ARC, assign was the default property ownership qualifier; but with ARC enabled, the default for retainable object pointer types is strong. (For scalars and other pointer types, assign is still the default.)

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