使用getter =的点语法与方法语法 [英] dot syntax vs method syntax with getter=

问题描述

我不确定这个问题有多少用途，但对我来说似乎很有趣...

I'm not sure how much use this question is but it seems interesting to me...

我认为使用property/synthesize语句等效于创建getter/setter.因此

I thought that using property/synthesize statements was equivalent to me creating the getter/setter. Therefore

// .h
@property (nonatomic) BOOL on;

// .m
@synthesize on = _on;

// In my mind synthesizes the following methods

// - (BOOL)on;
// - (void)setOn:(BOOL)on;

但是，如果我将声明更改为以下内容:

However if I change the declarations to the following:

                              v
@property (nonatomic, getter=isOn) BOOL on;

@synthesize on = _on;

// In my mind synthesizes the following

// - (BOOL)isOn;
// - (void)setOn:(BOOL)on;

然后鉴于以上所述，我覆盖了吸气剂，所以我知道它何时被调用:

Then given the above I override the getter so I know when it is called:

- (BOOL)isOn;
{
    NSLog(@"I was called");
    return _on;
}

现在在实例(myClass)上调用以下内容会导致:

Now calling the following on an instance (myClass) results in:

NSLog(@"%d", [myClass isOn]);

//=> 2012-02-09 22:18:04.818 Untitled[1569:707] I was called
//=> 2012-02-09 22:18:04.820 Untitled[1569:707] 1

NSLog(@"%d", myClass.isOn);

//=> 2012-02-09 22:18:24.859 Untitled[1599:707] I was called
//=> 2012-02-09 22:18:24.861 Untitled[1599:707] 1

NSLog(@"%d", myClass.on);         // This is the one I didn't expect to work

//=> 2012-02-09 22:18:55.568 Untitled[1629:707] I was called
//=> 2012-02-09 22:18:55.570 Untitled[1629:707] 1

我一直认为，如果我在这种意义上使用属性，那么使用带有点语法的getter/setter格式是完全有效的

I had always assumed that if I was using a property in this sense it was perfectly valid to use the getter/setter with dot syntax in the form

myClass.isOn;
myClass.on = on;

从另一个问题建议使用点语法时，应使用如下属性名称:

From another question it was suggested that when using dot syntax I should use the property name like this:

myClass.on   // Correct
myClass.isOn // Incorrect

尽管这可行，但逻辑上似乎有点不合逻辑，因为我知道没有底层方法- (BOOL)on，而是将其映射到- (BOOL)isOn

Although this works it seem slightly less logical because I know there is no underlying method - (BOOL)on it is instead mapped to - (BOOL)isOn

我的问题是(使用后面的示例)

My questions are (using the latter example)

• 这是错误还是应该myClass.on真正更改为调用- (BOOL)isOn
• 从严格意义上讲，我正在访问状态而不是调用行为，所以我当前使用的点语法正确吗? (例如myClass.isOn)

• Is this a bug or should myClass.on really be silently changed to call - (BOOL)isOn
• Semantically speaking I am accessing state not invoking behaviour so is my current use of dot syntax correct? (e.g. myClass.isOn)

尽管没有人明确地说过，我认为使用.isOn是不好的形式，因为无论在幕后调用相同方法的事实如何，语义上isOn都在问一个问题，这是更多的行为，而不是比国家.

Although no one has explicitly said it I have reasoned that using .isOn is bad form because regardless of the fact that under the hood the same method is called, semantically isOn is asking a question, which is more behaviour rather than state.

但是，我仍然不清楚魔术"接线的位置，从而将对myClass.on的调用转换为[myClass isOn]

However I am still unclear on where the "magic" wiring goes on that turns calls to myClass.on into [myClass isOn]

查看了更多文档后，我在

After looking around the docs some more I found this section on Declared Properties. Using the following code I can inspect a class' properties:

id MyClass = objc_getClass("MyClass");
unsigned int outCount, i;

objc_property_t *properties = class_copyPropertyList(MyClass, &outCount);
for (i = 0; i < outCount; i++) {
    objc_property_t property = properties[i];
    NSLog(@"Name: %s, attributes: %s\n", property_getName(property), property_getAttributes(property));
}

//=> 2012-02-10 07:10:28.333 Untitled[934:707] Name: on, attributes: Tc,GisOn,V_on

因此，我们具有以下属性:

So we have the following attributes:

• name = on
• type = char(Tc)
• getter = isOn(GisOn)
• 变量= _on(V_on)

所有这些信息都可以在运行时使用时，问题就出在运行时还是在编译时进行了查找，就像一些答案所建议的那样?

With all of this information available at runtime it kind of leaves the question is this lookup done at runtime or compile time like some answers suggest?

推荐答案

但是，我仍然不清楚魔术"接线的位置，从而将对myClass.on的调用转换为[myClass isOn]

However I am still unclear on where the "magic" wiring goes on that turns calls to myClass.on into [myClass isOn]

在获取上下文中编译obj.name时，逻辑肯定如下:

The logic surely goes as follows, when compiling an obj.name in a getting context:

if(there is an accessible @property for name in scope)
{
   if(there is a custom getter specified)
      compile "[obj customGetter]"
   else
      compile "[obj name]"
}
else if (there is an an accessible instance method name in scope)
   compile "[obj name]"
else
{
   compile "[obj name]"
   warn obj may not respond to name
}

语言/执行环境可以通过其他方式处理自定义getter名称，但是鉴于Obj-C将声明放在标头(公共)中，以上是关于自定义getter逻辑在何处执行的很好的猜测-编译呼叫站点时.

There are other ways a language/execution environment can handle custom getter names, but given that Obj-C puts the declaration in the header (which is public) the above is a good guess as to where the custom getter logic is performed - when compiling the call site.

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