可以不申报ivar但是用于合成？ [英] feasible to not declare ivar but use in synthesize?

问题描述

我正在查看一些示例代码，我对缺乏特定ivar的声明感到困惑。希望有人可以帮助我更好地理解这一点：

I'm looking at some sample code and I'm puzzled over the lack of declaration of a specific ivar. Hoping someone can help me understand this better:

typedef NSUInteger (^NumberOfItemsInSection)(ViewClass *viewClass, NSUInteger section);

// class declaration    
@interface SampleScrollView : UIScrollView
@property (nonatomic, copy) NumberOfItemsInSection itemsSectionBlock;
@end

// class implementation
@implementation SampleScrollView

@synthesize itemsSectionBlock = _itemsSectionBlock;

- (void)setItemsSectionBlock:(NumberOfItemsInSection)itemsSectionBlock
{
    // _itemsSectionBlock is not declared any where in the class 
    // How does the compiler not complain?

    _itemsSectionBlock = [itemsSectionBlock copy];
    [self reloadData];
}

@end

实例变量_itemsSectionBlock ，不会在任何地方声明，它只能在属性的setter覆盖中使用。这是如何工作的？

The instance variable, "_itemsSectionBlock", is not declared any where and it can just be used in the property's setter override. How does that work?

推荐答案

它是现代运行时的一部分，并减少了代码的重复 - 声明iVars然后声明这些iVars的属性。

It's part of the modern runtime, and cuts down on the duplication of code - declaring iVars and then declaring properties for those iVars.

它是由 @synthesize

现代运行时允许你做其他以前不能做的事情。例如，您现在可以在.m文件中声明iVars作为类扩展的一部分，这会减少您在公共接口中公开的信息量。

The modern runtime lets you do other things that you thought you couldn't do before. For example, you can now declare iVars in the .m file as part of a class extension, which reduces the amount of information you expose in your public interface.

更新

现代LLVM 4编译器甚至可以让您取消@sytnthesize行。如果您声明一个属性，它将为您自动合成，它甚至会创建一个带有前导下划线的后备存储。

The modern LLVM 4 compiler even lets you do away with the @sytnthesize line. If you declare a property it will auto-synthesize for you and it will even create a backing store with a leading underscore.

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