Swift 编程思想 阅读笔记

Swift 编程思想，第一部分：拯救小马html, body {overflow-x: initial !important;}.CodeMirror { height: auto; }
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Swift 编程思想链接Swift 编程思想，第一部分：拯救小马Swift 编程思想，第二部分：数组的 Map 方法Swift编程思想 第三部分：结构体和类Swift 编程思想 第四部分:全部使用map方法

Swift 编程思想

链接

http://alisoftware.github.io/swift/2015/09/06/thinking-in-swift-1/

http://alisoftware.github.io/swift/2015/09/20/thinking-in-swift-2/

http://alisoftware.github.io/swift/2015/10/03/thinking-in-swift-3/

http://alisoftware.github.io/swift/2015/10/11/thinking-in-swift-4/

http://swift.gg/2015/09/29/thinking-in-swift-1/

http://swift.gg/2015/10/09/thinking-in-swift-2/

http://swift.gg/2015/10/20/thinking-in-swift-3/

http://swift.gg/2015/10/22/thinking-in-swift-4/

Swift 编程思想，第一部分：拯救小马

问题:

• 隐式解析可选类型
• 强制转型
• 强制使用try
• 数组的使用

方案:

• 使用guard xxx else
• if let xx=yy{}
• [ListItem],数组的创建,返回,引用

Swift 编程思想，第二部分：数组的 Map 方法

主要讲了怎么使用map,faltMap

• map ,U->T,对数组每个元素操作,形成新的数据
• faltMap,U->T? 某个元素失败,不会加入最后的数组.

Swift编程思想 第三部分：结构体和类

• struct 值传递
• class 引用类型

Swift的结构体(structs)和类(Class)具有相同的功能 - 除了继承 - 结构体是值类型(value-types) (所以每一次变量赋值都是通过值拷贝的形式，与Int类型很相像)，而类属于引用类型(reference-types)，以引用方式传递而非值拷贝，这和Objective-C(以及OC中无处不在的难看的*，也代表着引用)中一样。

• 联合操作符

??操作符和ObjC的opt ?: val表达式很像，了解它的人都知道：opt ?? val如果在opt非空的时候返回它的值，如果是nil的话会返回val。这意味着如果opt是T?类型，val则必须是T类型，整个表达式的结果也会是T类型。

Swift 编程思想 第四部分:全部使用map方法

• 数组应用map方法

// 作用在Array<T>上的方法
    map( transform: T ->          U  ) -> Array<U>
flatMap( transform: T ->    Array<U> ) -> Array<U>

• 在可选类型上应用

// 作用在Optional<T>上的方法
    map( transform: T ->          U  ) -> Optional<U>
flatMap( transform: T -> Optional<U> ) -> Optional<U>

那么map方法到底对Optional类型(也叫做T?)做了什么？

其实很简单：和作用在Array上的一样，map方法将Optional中的内容取出来，用指定的transform: T->U方法做出转换，然后把结果包装成一个新的Optional。

如果细想一下，这和Array.map做的事情十分相似：这个方法对Array(与之相应的是Optional)中的每个元素使用transform函数转换，并将转换过的值封装在一个新的Array中(与之相应的是Optional)，作为结果返回

• 把 init 当闭包来用

let iconName = itemDesc["icon"] as? String
let icon = iconName.flatMap { UIImage(named: $0) }

let iconName = itemDesc["icon"] as? String
item.icon = iconName.flatMap(UIImage.init)

let iconName = itemDesc["icon"] as? String
item.icon = iconName.flatMap { imageName in UIImage(named: imageName) }

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