docs: clang 插件开发

Chapter1 - iOS/1.122.md

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+# Swift 字面量本质
+
+## 常见的字面量默认类型
+
+- `public typealias IntegerLiteralType = Int`
+- `public typealias FloatLiteralType = Float`
+- `public typealias BooleanLiteralType = Bool`
+- `public typealias StringLiteralType = String`
+
+可以通过 typealias 修改字面量的默认类型，Demo 如下：
+
+```swift
+typealias IntegerLiteralType = UInt8
+var val = 8
+val
+```
+
+<img src="https://github.com/FantasticLBP/knowledge-kit/raw/master/assets/SwiftChangeLiteral.png" style="zoom:25%">
+
+
+
+## 字面量协议
+
+Swift 自带的数据类型基本都可通过字面量初始化，本质原因是遵循了对应的协议
+
+|               |                                                        |                                                              |
+| ------------- | ------------------------------------------------------ | ------------------------------------------------------------ |
+| Bool          | ExpressibleByBooleanLiteral                            | var b:Bool = false                                           |
+| Int           | ExpressibleByIntegerLiteral                            | var num:Int = 2                                              |
+| Float、Double | ExpressibleByIntegerLiteral、ExpressibleByFloatLiteral | var height:Float = 175  <br>var height1:Float = 175.2 <br>var weight:Double = 130 <br>var weight1:Double = 130.1 |
+| Dictionary    | ExpressibleByDictionaryLiteral                         | var dic:Dictionary = ["name": "FantasticLBP"]                |
+| String        | ExpressibleByStringLiteral                             | var name:String = "FantasticLBP"                             |
+| Array、Set    | ExpressibleByArrayLiteral                              | var arr:Array = [1, 2, 3]                                    |
+| Optional      | ExpressibleByNilLiteral                                | var o:Optional<Int> = nil                                    |
+
+
+
+## 字面量协议的使用
+
+Demo1
+
+```swift
+extension Int : ExpressibleByBooleanLiteral {
+    public init(booleanLiteral value: Bool) {
+        self = value ? 1 : 0
+    }
+}
+var num: Int = true
+print(num)	// 1
+num = false
+print(num)	// 0
+```
+
+Demo2
+
+```swift
+class Student: ExpressibleByIntegerLiteral, ExpressibleByFloatLiteral, ExpressibleByStringLiteral, CustomStringConvertible {
+    var name: String = ""
+    var score: Double = 0
+    
+    required init(floatLiteral value: FloatLiteralType) {
+        self.score = value
+    }
+    required init(stringLiteral value: StringLiteralType) {
+        self.name = value
+    }
+    required init(integerLiteral value: IntegerLiteralType) {
+        self.score = Double(value)
+    }
+    required init(extendedGraphemeClusterLiteral value: String) {
+        self.name = value
+    }
+    required init(unicodeScalarLiteral value: String) {
+        self.name = value
+    }
+    var description: String {
+        "name is \(self.name), score is \(self.score)"
+    }
+}
+
+var student: Student = "杭城小刘"
+print(student)	// name is 杭城小刘, score is 0.0
+student = 100
+print(student)  // name is , score is 100.0
+```
+