swift字符类型Character

1. 什么是字符？

字符(Character)就是一个简单的符号（字母:abc, 数组:123等）。在swift种使用如下方式定义字符类型，

let someCharacter: Character

1.1 怎样定义字符并赋值

为字符串赋值可以通过let aStr: String = " "，为字符赋值也是一样，let aCharacter: Character = " "但是一个字符变量只能包含一个空格。

所以，如果你定义的变量包含多个字符，则应该使用String，而不是Character。

1.1.1 举例1: 定义并赋值字符

let someCharacter: Character = "H"
let specialCharacter: Character = "@" // 特殊字符
print(someCharacter)
print(specialCharacter)

1.1.2 举例2: 定义字符，并赋值多个字符（报错）

如果尝试为一个字符变量赋值两个字符，则会报错，如下代码所示，

let fialableCharacter: Character = @"H@"
// 用String类型替代Character
let okString: String = @"H@"

1.2 使用unicode和转移字符创建Character

开发这可以使用unicode创建特殊的字符类型，例如创建emoji表情字符。创建一个unicode需要使用转移字符，例如\u{n}，n是十六进制的数字。如下代码所示，

let heartShape: Character = "\u{2655}"
print(heartShape)
// 输出：♥

在这个例子总，一个星形的字符使用U+2655 unicode创建。虽然"{2655}"包裹在双引号种，编译器并不会把它当作字符串，因为我们使用了“转移字符{u}”。一个转移字符并不代表它字面上的含义。

2. 字符常用扩展属性和方法

如下方法参考github的SwifterSwift项目，读者可查看了解更多的细节。

import UIKit
// MARK: - Properties
public extension Character {
    /// Check if character is emoji
    /// - example: Character("😊").isEmoji -> true
    public var isEmoji: Bool {
        let scalarValue = String(self).unicodeScalars.first!.value
        switch scalarValue {
            case 0x3030, 0x00AE, 0x00A9, // Special Character > 特殊字符
            0x1D000...0x1F77F, // Emoticons > 情感符
            0x2100...0x27BF, // Misc symbols and Dingbats >
            0xFE00...0xFE0F, // Variation Selectors > 变异选择符
            0x1F900...0x1F9FF: // Supplemental Symbols and Pictographs > 补充的符号和象形文字
            return true
        default:
            return false
        }
    }
    
    /// Check if character is number
    /// - example: Character("1").isNummber
    public var isNumber: Bool {
        return Int(String(self)) != nil
    }
    
    /// Check if character is a letter(字母)
    /// - example: (1) Character("4").isLetter -> false, (2) Character("a").isLetter -> True
    public var isLetter: Bool {
        return String(self).rangeOfCharacter(from: .letters, options: .numeric, range: nil) != nil
    }
    
    /// Check if character is lowercased
    /// - example: (1) Character("a").isLowercased -> true, (2) Character("A").isLowercased -> false
    public var isLowercased: Bool {
        return String(self) == String(self).lowercased()
    }
    
    /// Check if character is uppercased
    /// - example: (1) Character("a").isUppercased -> true, (2) Character("A").isUppercased -> true
    public var isUppercased: Bool {
        return String(self) == String(self).uppercased()
    }
    
    /// Check if character is white space(空格)
    /// - example: (1) Character(" ").isWhiteSpace -> true, (2) Character("A").isWhiteSpace -> false
    public var isWhiteSpace: Bool {
        return String(self) == " "
    }
    
    /// Integer value from character (if applicable)
    /// - example: (1) Character("1").int -> 1, (2) Character("A").int -> nil
    public var int: Int? {
        return Int(String(self))
    }
    
    // String value from character
    public var string: String {
        return String(self)
    }
    
    /// Return the character lowercased
    public var lowercased: Character {
        return String(self).lowercased().first!
    }
    
    /// Return the character uppercased
    public var uppercased: Character {
        return String(self).uppercased().first!
    }
}


// MARK: - Methods
public extension Character {
    /// Random character
//    public static func randomAlphanumeric() -> Character {
//        return "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789".randomElement()!
//    }
}

// MARK: - Operater
public extension Character {
    /// Repeat character multiple times
    /// - example: Character("=") * 10 -> "=========="
    /// - Parameters:
    ///     - lhs: charater to repeat.
    ///     - rhs: number of times to repeat character.
    /// - Returns: strign with charater repeated n times.
    public static func * (lhs: Character, rhs: Int) -> String {
        guard rhs > 0 else { return "" }
        return String(repeating: String(lhs), count: rhs)
    }
    
    /// Repeat character mltiple tiems
    /// - exmaple: 10 * Character("-") -> "----------"
    /// - Parameter:
    ///     - lhs: number of times to repeat character.
    ///     - rhs: character to repeat
    /// - Returns: string with character repeated n times
    public static func * (lhs: Int, rhs: Character) -> String {
        guard lhs > 0 else { return "" }
        return String(repeating: String(rhs), count: lhs)
    }
}