带下划线前缀的综合属性和变量:这是什么意思? [英] Synthesized property and variable with underscore prefix: what does this mean?

问题描述

可能的重复:
属性名称的下划线前缀?

这是什么意思?@synthesize window=_window; 我知道一般来说这意味着某个类"有一个窗口，但为什么使用 _window 而不是 window>?这是命名空间的事情吗?

What does this mean? @synthesize window=_window; I know that in general it means that 'some class' has a window, but why use _window instead of just window? Is this a namespace thing?

推荐答案

我将尝试用基本的英语描述这个编程约定.

I'll give a go at describing this programming convention in basic English.

在其他语言中，使用m、m_ 或_ 来命名成员变量是一种非常常见的约定，以区别于它们本地声明的变量，并表示它们应该在必要时编写访问器(没有 classInstance.m_Variable = 5).

It is a very common convention in other languages to name member variables with a preceding m, m_, or _ to distinguish them from locally declared variables and to signify that they should have accessors written, if necessary (no classInstance.m_Variable = 5).

如果一个 Objective-C 程序员按照这个约定(他们应该)声明 ivars 并使用基本语法 @synthesize _window; 那么属性的用法就变得有些难看:classInstance._window = myWindow 或 [classInstance set_window:myWindow].使用语法 @synthesize window=_window; 允许 Obj-C 程序员利用流行的编程标准(在 ivars 之前带有 _)，同时拥有使用 Apple 的属性访问器标准 classInstance.window = myWindow 和 [classInstance setWindow:myWindow].

If an Objective-C programmer declares ivars following this convention (and they should) and uses the basic syntax @synthesize _window; then the usage for the property becomes somewhat ugly: classInstance._window = myWindow or [classInstance set_window:myWindow]. Using the syntax @synthesize window=_window; allows the Obj-C programmer to utilize a popular programming standard (preceding ivars with _) while simultaneously having property accessors that use the Apple standard classInstance.window = myWindow and [classInstance setWindow:myWindow].

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