.Type

The metatype of a class,structure,or enumeration type is the name of that type followed by .Type. The metatype of a protocol type—not the concrete type that conforms to the protocol at runtime—is the name of that protocol followed by .Protocol. For example,the metatype of theclass?type?SomeClass?is?SomeClass.Type?and the metatype of the?protocol?SomeProtocol?is?SomeProtocol.Protocol.

_{From Apple :?metaType Type}

Under the hood?AnyClass?is

Basically where ever you see?AnyClass,?Any.Type,?AnyObject.Type,its because it‘s in need of a type. A very very common place we see it is when we want to?register?a class for our tableView using?register?func.

_{If you are confused as to what does ‘Swift.‘ do then above,then see the comments from?here}

The above could have also been written as:

.self

You can use the?postfix?self expression to access a type as a value. For example,SomeClass.self returns SomeClass itself,?not?an instance of SomeClass. And SomeProtocol.self returns SomeProtocol itself,?not?an instance of a type that conforms to SomeProtocol at runtime. You can use a type(of:) expression with an instance of a type to access that instance’s dynamic,runtime type as a value,as the following example shows:

_{From Apple :?metaType Type}

Where is it used?

If you are writing/creating a function that accepts a?type?e.g. class,?not?an instance then to you would write?T.Type?as the type of the parameter. What it expects as a parameter can be:?String.self,?CustomTableView.self,?someOtherClass.self.

In continuation of the tableView code:

Playground code:

?

Easy example

struct Something {

? ? var x = 5

}

?

let a = Something()

type(of:a) == Something.self // true

Hard example

class SomeBaseClass {

? ? class func printClassName() {

? ? ? ? print("SomeBaseClass")

? ? }

}

class SomeSubClass: SomeBaseClass {

? ? override class func printClassName() {

? ? ? ? print("SomeSubClass")

? ? }

}

?

?

let someInstance: SomeBaseClass = SomeSubClass()

/*? ? ? ? ? ? ? ? ? ? ? |? ? ? ? ? ? ? ? |

? ? ? ? ? ? ? ? ? ? compileTime ? ? ? Runtime

? ? ? ? ? ? ? ? ? ? ? ? |? ? ? ? ? ? ? ? |?

To extract,use: ? ? ? .self? ? ? ? ? type(of)

?

? The compile-time type of someInstance is SomeBaseClass,

? and the runtime type of someInstance is SomeSubClass */

?

type(of: someInstance) == SomeSubClass.self // TRUE

type(of: someInstance) == SomeBaseClass.self // FALSE

I highly recommend to read?Apple documentation on Types. Also see?here

?

https://stackoverflow.com/questions/31438368/swift-whats-the-difference-between-metatype-type-and-self