Swift extension (Extensions) (14)

You can add new features to a class

UIViewController

UIViewController {    // 为 UIViewController 添加的新功能写到这里}

Double

Extension Double {varkm:double {return  Self * 1_000. 0}varm:double {return  Self}varcm:double {return  Self / 100.0}varmm:double {return  Self / 1_000. 0}var ft: Double {return  Self / 3.28084}varsq:double {return  Self *  Self}}

ViewControllerCustom

extension ViewController{    printfChars()    {        print("I am char")    }}

Two-variable instance method (mutating Instance Methods)

An instance method that is added by extension can also modify the instance itself. A method that modifies self or its properties in a struct and enumeration type must label the instance method as mutating, just as a mutable method from the original implementation.
The following example adds a variable method named Square to the Int type of Swift to calculate the square value of the original value:
改变Int 值本身

Int {    mutating func square() {        selfselfself    }}

Three nested types (Nested Types)

Extensions can add new nested types for existing classes, structs, and enumerations:

extension Int {    enum Kind {        case Negative, Zero, Positive    }    var kind: Kind {        switch self {        case0:            return .Zero        caseletwhere0:            return .Positive        default:            return .Negative        }    }}

In Viewcontroller
In Viewdidload

 Self. Printfchars () Let Oneinch =25.4. mmPrint("one inch is \ (oneinch) meters")//One inch is 0.0254 metersLet Dou =23.4. sqPrint("\ (Dou)")//547.56Let numbers = [1,2,4,5,6,3,0,- Wu,- $] Self. Printintegerkinds (Numbers)//+ + + + + + 0--varIntnumb =5Intnumb.square ()Print("\ (intnumb)")///

This example Int adds a nested enumeration. This named Kind enumeration represents the type of a particular integer. Specifically, it means that integers are positive, 0, or negative.
This example also Int adds a computed instance property, that is, to Kind return the appropriate enumeration member based on an integer Kind .
Now, this nested enumeration can be used with any Int value:

Func Printintegerkinds (numbers: [Int]) { forNumberinchNumbers {SwitchNumber.kind { Case.Negative:Print("- ",Terminator:"") Case.Zero:Print("0",Terminator:"") Case.Positive:Print("+ ",Terminator:"")            }        }Print("")    }

Swift extension (Extensions) (14)