Swift development fifth-four points of knowledge (Struct mutable method &tuple&autoclosure&optional Chain)

This article is divided into three parts:

One, the Struct mutable method Two, the plural group (Tuple) use three, the autoclosure use four, Optional Chain use

Mutable method of Struct

Directly on the code:

struct User {    var weight:int    var height:int        //  will error left side of mutating operator isn ' t mu Table: ' Self ' is immutable    //  because the Struct-out variable is immutable, you have to add a keyword when you want to use a method to change the value in a variable mutating      mutating func gainweight (newweight:int) {        + =    newweight117 178 ) newuser.gainweight (ten)

Operation Result:

Second, multivariate group (tuple)

Multi-Group is a new feature of Swift, the common programmer is to define a temporary variable to save the need to exchange the value, now we can use the Multi-group attribute without extra space to directly exchange A and B values

Func swapme<t>(inout a:t, inout b:t) {    =56Swapme (&a, B: & Amp b) Print (A, B)  //Output result is 6 5

Third, the basic use of autoclosure

//without the use of autoclosureFunc logiftrue (predicate: ()Bool) {    ifpredicate () {print ("True")    }}//The first method of invocationlogiftrue {(), Boolinch    return true}//The second method of invocationLogiftrue ({return 2>1})//The third method of invocationLogiftrue ({2>1})//Fourth method of invocationlogiftrue{2>1}//using AutoclosureFunc logiftrue (@autoclosure predicate: ()Bool) {    ifpredicate () {print ("True")    } Else{print ("False")    }}//Invocation ModeLogiftrue (2>1) Logiftrue (1>2)

iv. use of Optional Chain

class Toy {Let    name:string    init (name:string) {        = name    }}class  Pet {    var toy:toy? }class child {    var pet:pet?  ""  == Child ()

The last access here is name, and in the definition of Toy, name is defined as a string rather than a string? , but the toyname we get is actually a String type. Is this because in Optional Chaining we are in any one? Can meet nil and return early, this time of course you can only get nil.

Let Toyname = Xiaoming.pet?. Toy? . Name // so in actual development, we usually use Optional Binding to directly value: if let Toyname = Xiaoming.pet?. Toy? . Name {    ///  then Toyname is a string instead of a string? }extension Toy {    func play () {        pri NT (" Play Toys ~ ~")    in    child.pet?. Toy? . Play ()}

Swift development fifth-four points of knowledge (Struct mutable method &tuple&autoclosure&optional Chain)