blocks|key|2740576|text|首先，[NSString+class]的Swift等价物是.self+(参见Metatype+docs，尽管它们都很薄)。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2740577|事实上，NSString.class甚至不能工作！您必须使用NSString.self。|2740578|let+s+=+NSString.self
var+str+=+s()
str+=+"asdf"|code-block|syntax|javascript|2740579|类似地，我尝试了一个快速类...|2740580|class+MyClass+{

}

let+MyClassRef+=+MyClass.self

//+ERROR+:(
let+my_obj+=+MyClassRef()|2740581|嗯，…错误信息为：|2740582|2740583|游乐场执行失败:+error：:16:1:+error：：error:构造具有元类型值的类类型'X‘的对象需要'@required’初始值设定项|blockquote|2740584|2740585|Y().me()+%5E+:3:7:注意:选择了类型为'()‘的隐式初始值设定项X{%5E|2740586|2740587|我花了一段时间才弄明白这是什么意思，…结果是它想让这个类有一个@required+init()|2740588|class+X+{
++++func+me()+{
++++++++println("asdf")
++++}

++++required+init+()+{

++++}
}

let+Y+=+X.self

//+prints+"asdf"
Y().me()|2740589|一些文档将其称为.Type，但MyClass.Type在游乐场上给了我一个错误。|2740590|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/doc/uid/TP40014097-CH31-XID_1022^0|3|G|T|5|12|D|0|0|4|E|U|D|0|0|0|0|0|0|0|0|0|0|V|G|0|0|8|5|F|C|0^^$0|@$1|2|3|4|5|6|7|1E|8|@$9|1F|A|1G|B|C]|$9|1H|A|1I|B|C]]|D|@$9|1J|A|1K|1|1L]]|E|$]]|$1|F|3|G|5|6|7|1M|8|@$9|1N|A|1O|B|C]|$9|1P|A|1Q|B|C]]|D|@]|E|$]]|$1|H|3|I|5|J|7|1R|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|1S|8|@]|D|@]|E|$]]|$1|O|3|P|5|J|7|1T|8|@]|D|@]|E|$K|L]]|$1|Q|3|R|5|6|7|1U|8|@]|D|@]|E|$]]|$1|S|3|-4|5|6|7|1V|8|@]|D|@]|E|$]]|$1|T|3|U|5|V|7|1W|8|@]|D|@]|E|$]]|$1|W|3|-4|5|6|7|1X|8|@]|D|@]|E|$]]|$1|X|3|Y|5|6|7|1Y|8|@]|D|@]|E|$]]|$1|Z|3|-4|5|6|7|1Z|8|@]|D|@]|E|$]]|$1|10|3|11|5|6|7|20|8|@$9|21|A|22|B|C]]|D|@]|E|$]]|$1|12|3|13|5|J|7|23|8|@]|D|@]|E|$K|L]]|$1|14|3|15|5|6|7|24|8|@$9|25|A|26|B|C]|$9|27|A|28|B|C]]|D|@]|E|$]]|$1|16|3|-4|5|6|7|29|8|@]|D|@]|E|$]]]|17|$18|$5|19|1A|1B|E|$1C|1D]]]]

Well, for one, the Swift equivalent of <code>[NSString class]</code> is <code>.self</code> (see <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/doc/uid/TP40014097-CH31-XID_1022">Metatype docs</a>, though they're pretty thin).

In fact, <code>NSString.class</code> doesn't even work! You have to use <code>NSString.self</code>.

<pre><code>let s = NSString.self
var str = s()
str = "asdf"
</code></pre>

Similarly, with a swift class I tried...

<pre><code>class MyClass {

}

let MyClassRef = MyClass.self

// ERROR :(
let my_obj = MyClassRef()
</code></pre>

Hmm… the error says:

<blockquote>
 Playground execution failed: error: :16:1: error: constructing an object of class type 'X' with a metatype value requires an '@required' initializer

<pre><code> Y().me()
 ^
 &lt;REPL&gt;:3:7: note: selected implicit initializer with type '()'
 class X {
 ^
</code></pre>
</blockquote>

It took me a while to figure out what this means… turns out it wants the class to have a <code>@required init()</code>

<pre><code>class X {
 func me() {
 println("asdf")
 }

 required init () {

 }
}

let Y = X.self

// prints "asdf"
Y().me()
</code></pre>

Some of the docs refer to this as <code>.Type</code>, but <code>MyClass.Type</code> gives me an error in the playground.

blocks|key|155559|text|如果我没看错文档，如果你处理实例，例如，想要返回一个与给定对象相同类型的新实例，并且该类型可以用init()构造，你可以这样做：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|155560|let+typeOfObject+=+aGivenObject.dynamicType
var+freshInstance+=+typeOfObject()|code-block|syntax|javascript|155561|我用String快速测试了一下：|155562|let+someType+=+"Fooo".dynamicType
let+emptyString+=+someType()
let+threeString+=+someType("Three")|155563|它工作得很好。|155564|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

If I'm reading the documentation right, if you deal with instances and e.g. want to return a new instance of the same Type than the object you have been given and the Type can be constructed with an init() you can do:

<pre><code>let typeOfObject = aGivenObject.dynamicType
var freshInstance = typeOfObject()
</code></pre>

I quickly tested it with String:

<pre><code>let someType = "Fooo".dynamicType
let emptyString = someType()
let threeString = someType("Three")
</code></pre>

which worked fine.

blocks|key|156862|text|总算有点用了。这有点懒，但即使是NSClassFromString()方法对我也不起作用…|type|unstyled|depth|inlineStyleRanges|entityRanges|data|156863|import+Foundation

var+classMap+=+Dictionary<String,+AnyObject>()

func+mapClass(name:+String,+constructor:+AnyObject)+->+()
{
++++classMap[name]+=+constructor;
}

class+Factory
{
++++class+func+create(className:+String)+->+AnyObject?
++++{
++++++++var+something+:+AnyObject?

++++++++var+template+:+FactoryObject?+=+classMap[className]+as?+FactoryObject

++++++++if+(template)
++++++++{
++++++++++++let+somethingElse+:+FactoryObject+=+template!.dynamicType()

++++++++++++return+somethingElse
++++++++}

++++++++return+nil
++++}
}


+import+ObjectiveC

+class+FactoryObject+:+NSObject
{
++++@required+init()+{}
//...
}

class+Foo+:+FactoryObject
{
++++class+override+func+initialize()
++++{
++++++++mapClass("LocalData",+LocalData())
++++}
++++init+()+{+super.init()+}
}

var+makeFoo+:+AnyObject?+=+Factory.create("Foo")|code-block|syntax|javascript|156864|对了，"makeFoo“包含一个Foo实例。|156865|缺点是您的类必须从FactoryObject派生，并且它们必须具有Obj-C+%2Binitialize方法，以便您的类通过全局函数"mapClass“自动插入到类映射中。|156866|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Finally got something to work. Its a bit lazy but even the NSClassFromString() route did not work for me...

<pre><code>import Foundation

var classMap = Dictionary&lt;String, AnyObject&gt;()

func mapClass(name: String, constructor: AnyObject) -&gt; ()
{
 classMap[name] = constructor;
}

class Factory
{
 class func create(className: String) -&gt; AnyObject?
 {
 var something : AnyObject?

 var template : FactoryObject? = classMap[className] as? FactoryObject

 if (template)
 {
 let somethingElse : FactoryObject = template!.dynamicType()

 return somethingElse
 }

 return nil
 }
}


 import ObjectiveC

 class FactoryObject : NSObject
{
 @required init() {}
//...
}

class Foo : FactoryObject
{
 class override func initialize()
 {
 mapClass("LocalData", LocalData())
 }
 init () { super.init() }
}

var makeFoo : AnyObject? = Factory.create("Foo")
</code></pre>

and bingo, "makeFoo" contains a Foo instance.

The downside is your classes must derrive from FactoryObject and they MUST have the Obj-C +initialize method so your class gets automagically inserted in the class map by global function "mapClass".

blocks|key|155623|text|下面是如何使用NSClassFromString。你必须知道你最终会得到什么超类。下面是一个超类-子类对，它们知道如何为println描述自身|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|155624|@objc(Zilk)+class+Zilk+:+NSObject+{
++++override+var+description+:+String+{return+"I+am+a+Zilk"}
}

@objc(Zork)+class+Zork+:+Zilk+{
++++override+var+description+:+String+{return+"I+am+a+Zork"}
}|code-block|syntax|javascript|155625|注意使用特殊的@obj语法来指定这些类的Objective-C参数名称；这是至关重要的，因为否则我们不知道指定每个类的参数字符串。|155626|现在，我们可以使用NSClassFromString来创建Zork类或Zilk类，因为我们知道可以将其作为NSObject类型，而不会在以后崩溃：|155627|let+aClass+=+NSClassFromString("Zork")+as+NSObject.Type
let+anObject+=+aClass()
println(anObject)+//+"I+am+a+Zork"|155628|而且它是可逆的；println(NSStringFromClass(anObject.dynamicType))也可以工作。|155629|155630|现代版本：|BOLD|155631|++++if+let+aClass+=+NSClassFromString("Zork")+as?+NSObject.Type+{
++++++++let+anObject+=+aClass.init()
++++++++print(anObject)+//+"I+am+a+Zork"
++++++++print(NSStringFromClass(type(of:anObject)))+//+Zork
++++}|155632|entityMap^0|7|H|1O|7|0|0|7|4|0|9|H|0|0|8|1C|0|0|0|5|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@$9|11|A|12|B|C]|$9|13|A|14|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|15|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|16|8|@$9|17|A|18|B|C]]|D|@]|E|$]]|$1|M|3|N|5|6|7|19|8|@$9|1A|A|1B|B|C]]|D|@]|E|$]]|$1|O|3|P|5|H|7|1C|8|@]|D|@]|E|$I|J]]|$1|Q|3|R|5|6|7|1D|8|@$9|1E|A|1F|B|C]]|D|@]|E|$]]|$1|S|3|-4|5|6|7|1G|8|@]|D|@]|E|$]]|$1|T|3|U|5|6|7|1H|8|@$9|1I|A|1J|B|V]]|D|@]|E|$]]|$1|W|3|X|5|H|7|1K|8|@]|D|@]|E|$I|J]]|$1|Y|3|-4|5|6|7|1L|8|@]|D|@]|E|$]]]|Z|$]]

Here's how to use <code>NSClassFromString</code>. You have to know the superclass of what you're going to end up with. Here are a superclass-subclass pair that know how to describe themselves for <code>println</code>:

<pre><code>@objc(Zilk) class Zilk : NSObject {
 override var description : String {return "I am a Zilk"}
}

@objc(Zork) class Zork : Zilk {
 override var description : String {return "I am a Zork"}
}
</code></pre>

Notice the use of the special <code>@obj</code> syntax to dictate the Objective-C munged name of these classes; that's crucial, because otherwise we don't know the munged string that designates each class.

Now we can use <code>NSClassFromString</code> to make the Zork class or the Zilk class, because we know we can type it as an NSObject and not crash later:

<pre><code>let aClass = NSClassFromString("Zork") as NSObject.Type
let anObject = aClass()
println(anObject) // "I am a Zork"
</code></pre>

And it's reversible; <code>println(NSStringFromClass(anObject.dynamicType))</code> also works.

<hr>

Modern version:

<pre><code> if let aClass = NSClassFromString("Zork") as? NSObject.Type {
 let anObject = aClass.init()
 print(anObject) // "I am a Zork"
 print(NSStringFromClass(type(of:anObject))) // Zork
 }
</code></pre>

blocks|key|2740796|text|这是另一个显示类层次结构实现的示例，类似于accepted，为Swift的第一个版本更新。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2740797|class+NamedItem+:+NSObject+{
++++func+display()+{
++++++++println("display")
++++}

++++required+override+init()+{
++++++++super.init()
++++++++println("base")
++++}
}

class+File+:+NamedItem+{
++++required+init()+{
++++++++super.init()
++++++++println("folder")
++++}
}

class+Folder+:+NamedItem+{
++++required+init()+{
++++++++super.init()
++++++++println("file")
++++}
}

let+y+=+Folder.self
y().display()
let+z+=+File.self
z().display()|code-block|syntax|javascript|2740798|打印此结果：|2740799|base
file
display
base
folder
display|2740800|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Here is another example showing class hierarchy implementation, similar to accepted answer, updated for the first release of Swift. 

<pre><code>class NamedItem : NSObject {
 func display() {
 println("display")
 }

 required override init() {
 super.init()
 println("base")
 }
}

class File : NamedItem {
 required init() {
 super.init()
 println("folder")
 }
}

class Folder : NamedItem {
 required init() {
 super.init()
 println("file")
 }
}

let y = Folder.self
y().display()
let z = File.self
z().display()
</code></pre>

Prints this result:

<pre><code>base
file
display
base
folder
display
</code></pre>

blocks|key|2740834|text|比较类型的快速实现|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|2740835|protocol+Decoratable{}
class+A:Decoratable{}
class+B:Decoratable{}
let+object:AnyObject+=+A()
object.dynamicType+is+A.Type//true
object.dynamicType+is+B.Type//false
object.dynamicType+is+Decoratable.Type//true|code-block|syntax|javascript|2740836|注意：注意，它还可以使用对象可以扩展或不可以扩展的协议|2740837|entityMap^0|5|4|0|0|0|R|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|S|8|@$9|T|A|U|B|C]]|D|@]|E|$]]|$1|M|3|-4|5|6|7|V|8|@]|D|@]|E|$]]]|N|$]]

<h2>Swift implementation of comparing types</h2>

<pre><code>protocol Decoratable{}
class A:Decoratable{}
class B:Decoratable{}
let object:AnyObject = A()
object.dynamicType is A.Type//true
object.dynamicType is B.Type//false
object.dynamicType is Decoratable.Type//true
</code></pre>

NOTE: Notice that it also works with protocols the object may or may not extend

blocks|key|155653|text|在swift+3中|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|155654|object.dynamicType|code-block|syntax|javascript|155655|已弃用。|155656|请改用：|155657|type(of:object)|155658|entityMap^0|1|7|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|V|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|W|8|@]|D|@]|E|$]]|$1|M|3|N|5|6|7|X|8|@]|D|@]|E|$]]|$1|O|3|P|5|H|7|Y|8|@]|D|@]|E|$I|J]]|$1|Q|3|-4|5|6|7|Z|8|@]|D|@]|E|$]]]|R|$]]

In swift 3 

<pre><code>object.dynamicType
</code></pre>

is deprecated.

Instead use:

<pre><code>type(of:object)
</code></pre>

I am trying to dynamically create a <code>class</code> instance based type using generics, however I am encountering difficulty with class introspection.

Here are the questions:

<ul>
<li>Is there a Swift-equivalent to Obj-C's <code>self.class</code>?</li>
<li>Is there a way to instantiate a class using the <code>AnyClass</code> result from <code>NSClassFromString</code>?</li>
<li>Is there a way to get <code>AnyClass</code> or otherwise type information strictly from a generic parameter <code>T</code>? (Similar to C#'s <code>typeof(T)</code> syntax)</li>
</ul>

Swift class introspection & generics

Objective-C

Swift

我正在尝试使用泛型动态创建一个基于class实例的类型，但是我在类自省方面遇到了困难。以下是问题：是否有一个与Obj-C的self.classIs等价的Swift?有没有办法使用NSClassFromStringIs的AnyClass结果实例化一个类?有没有办法严格地从泛型参数AnyClass中获取T或其他类型信息？(...

问Swift类自省和泛型
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