Topics Logical Values struct Bool A value type whose instances are either true or false. Numeric Values struct Int A signed integer value type. struct Double A double-precision, floating-point value type. struct Float A single-precision, floating-poi…

原文:Swift语言指南(六)--可选值 在值可能不存在的情况下使用可选值(optional), 可选值是: · 存在一个值,这个值等于 x 或 · 不存在任何值 注: 在 C 和 Objective-C 中可选值的概念并不存在.Objective-C 中(与可选值)最相近的(概念)是,一个以对象为返回值的方法,也可以返回 nil,nil表示“不存在有效的对象”.不过,这规则只对对象有效——对于结构.基本的 C 类型或枚举值无效.对于这些类型,Objective-C 语言的方法通常会返回一个特殊…

initial value:必须初始化.不影响观察者 Classes and structures must set all of their stored properties to an appropriate initial value by the time an instance of that class or structure is created. Stored properties cannot be left in an indeterminate state. You c…

1.Tuples are compared from left to right, one value at a time, until the comparison finds two values that aren’t equal. (1, "zebra") < (2, "apple") You can compare two tuples if they have the same type and the same number of values.…

总结:整个Closure的作用在于简化语言表述形式. 一.闭包的简化 Closure expression syntax has the following general form: { () -> in } reversedNames = names.sorted(by: { (s1: String, s2: String) -> Bool in return s1 > s2 }) Because the sorting closure is passed as an argumen…

一.变量定义 1.常量与变量 Use let to make a constant and var to make a variable. 2.类型与推测 However, you don’t always have to write the type explicitly. Providing a value when you create a constant or variable lets the compiler infer its type. 3.类型转换与字符串 Write the…

结论:value是拷贝,Reference是引用 Value and Reference Types Types in Swift fall into one of two categories: first, “value types”, where each instance keeps a unique copy of its data, usually defined as a struct, enum, or tuple. The second, “reference types”,…

一.数据类型 1.基础类型的封装 Swift provides its own versions of all fundamental C and Objective-C types, including Int for integers, Doubleand Float for floating-point values 2.新类型 Swift introduces advanced types not found in Objective-C, such as tuples. Tuples…

1.oc比较: -(BOOL) isKindOfClass: classObj判断是否是这个类或者这个类的子类的实例 -(BOOL) isMemberOfClass: classObj 判断是否是这个类的实例 2.is 类型检查 Use the type check operator (is) to check whether an instance is of a certain subclass type. 3. (as? or as!) 类型转化 Use the conditional f…

Swift defines two kinds of initializers for class types to help ensure all stored properties receive an initial value. These are known as designated initializers and convenience initializers. Designated:指定的:特指的 全初始化与部分初始化 Designated Initializers and…