How to write an extension of a qualified type for an array in Swift3

We know that Swift can extend existing classes or structures that can exist in a standard library (or a core library). If a struct is a collection type (such as an array), it is more interesting. We want to try to write an extension of a qualified type array so we take array< Int > For example.

This cat wants to be able to write like this:

Array<Int>{    //....}

However, it is clearly not possible to: [

Turned to Apple's official swift programming language and got nothing. So he went online and found a workable solution, a drop that must be used in the WHERE clause:

extension _ArrayType where Element == Int{    count(index:Int)->Int{        print("In _ArrayType")        return11*11    }}[1,2,3].count(2)["1"].count(2//error!!!

The main idea is that we can't operate directly with an array, but indirectly with the _arraytype type, you can see that the last line of code is wrong because it is an array of [String] type.

But don't be happy too early, the above code does not work in Swift3, because there is no way to find the _arraytype type in Swit3;(

Be okay, however, cannot start with an array, and we can indirectly start with the protocol it follows. So there are two ways to achieve this in Swift3:

extension Sequence where Iterator.Element == Int{    count(index:Int)->Int{        print("In Sequence")        returnindexindex    }}extension Collection where Iterator.Element == Int{    count(index:Int)->Int{        print("In Collection")        returnindexindex    }}

It is important to note that if you want to use the above code in swift2.x, you need to add type after sequence and collection:

SequenceTypeCollectionType

It is worth mentioning that if we want elements in an array extension to follow a protocol, rather than a certain type, you can write this:

protocol lovable{func fallinlove (with  name : String)}struct  Love : lovable{func fallinlove (with  name : String) {print  ( "fall in love with \ (name)" )}}extension Array where element : lovable{func count (index:int) ->  int{print  ( "in Array" ) return  Index * index}}let  loves = [Love (), Love ()]loves.count (index : 12 )  

How to write an extension of a qualified type for an array in Swift3