objective-c - Xcode中null相关的property属性有什么作用？

Question

在 Xcode 6.3 中，我注意到了一些属性，即:

• 非空
• null_resettable
• 可为空

有人可以解释一下他们在申请时做了什么吗？

Answer 1

Apple 添加了两个新的类型注释:

• __nullable 指针可能有一个nil 值，
• 虽然 __nonnull 不能有 nil 值

正如你应该知道的，在 Swift 中你可以使用 Ottionals，但在 Objective-C 中你不能。这些属性让您可以创建 Swift 更容易理解的 Objective-C 代码，编译器会在您违反规则时警告您，例如:

@property (copy, nullable) NSString *name;
@property (copy, nonnull) NSArray *allItems;

这将被迅速“翻译”为:

var name: String?
var allItems: [AnyObject]!

这取自NSHipster :

nonnull: Indicates that the pointer should/will never be nil. Pointersannotated with nonnull are imported into Swift as their non-optionalbase value (i.e., NSData).

nullable: Indicates that the pointer can be nil in general practice.Imported into Swift as an optional value (NSURL?).

null_unspecified: Continues the current functionality ofimporting into Swift as an implicitly unwrapped optional, ideally tobe used during this annotation process only.

null_resettable:Indicates that while a property will always have a value, it can bereset by assigning nil. Properties with a non-nil default value can beannotated this way, like tintColor. Imported into Swift as a(relatively safe) implicitly unwrapped optional. Document accordingly!