Swift: Swift 字符串与字符：String 类型详解与实用方法

let firstName = "Alice"
let lastName = "Johnson"
let product = "Premium Plan"
let price = "299.00"
let email = "Dear " + firstName + " " + lastName + ",\n\nThank you for purchasing " + product + "!\nYour payment: $" + price + ".\n\nBest regards,\nCharlie"

let firstName = "Alice"
let lastName = "Johnson"
let product = "Premium Plan"
let price = "299.00"
let email = """
Dear \(firstName) \(lastName),
Thank you for purchasing \(product)!
Your payment: $\(price).
Best regards,
Charlie
"""
print(email)

let greeting = "Hello, Swift!"
let empty = ""           // 空字符串
let emoji = "Swift"      // 包含 Unicode

let firstName = "Alice"
let lastName = "Johnson"
// 使用 + 拼接
let fullName = firstName + " " + lastName
print(fullName)  // Alice Johnson
// 使用 += 追加
var message = "Hello"
message += ", "
message += firstName
print(message)  // Hello, Alice
// 使用 append 方法
var greeting2 = "Welcome"
greeting2.append("!")
print(greeting2)  // Welcome!

// ============================================
// 从用户信息生成邮件地址
// 演示字符串创建和拼接
// ============================================
let domain = "@example.com"
let alice = "alice.johnson"
let bob = "bob.smith"
let charlie = "charlie.brown"
let email1 = alice + domain
let email2 = bob + domain
let email3 = charlie + domain
print(email1)
print(email2)
print(email3)
// 拼接完整 URL
let scheme = "https://"
let site = "api."
let fullURL = scheme + site + domain
print("API URL: \(fullURL)")

let name = "Alice"
let age = 28
let height = 1.75
let intro = "My name is \(name), I am \(age) years old and \(height) meters tall."
print(intro)
// My name is Alice, I am 28 years old and 1.75 meters tall.
// 插值中可以写表达式
let price = 29.99
let qty = 3
let summary = "Total: $\(price * Double(qty))"
print(summary)
// Total: $89.97

let text = "Hello, Swift!"
text.count                     // 13（字符数）
text.isEmpty                   // false
text.hasPrefix("Hello")        // true
text.hasSuffix("Swift!")       // true
text.uppercased()              // "HELLO, SWIFT!"
text.lowercased()              // "hello, swift!"
text.contains("Swift")         // true

// ============================================
// 生成格式化的用户信息卡片
// 演示字符串插值和常用方法
// ============================================
let firstName = "Alice"
let lastName = "Johnson"
let email = "alice.johnson@example.com"
let role = "Admin"
// 使用插值组合信息
let displayName = "\(firstName) \(lastName)"
let emailDomain = email.contains("@") ? email.split(separator: "@")[1] : "unknown"
// 验证格式
let isValidEmail = email.contains(".") && email.contains("@")
let isAdmin = role.uppercased() == "ADMIN"
print("=== User Card ===")
print("Name: \(displayName)")
print("Email: \(email)")
print("Domain: \(emailDomain)")
print("Valid Email: \(isValidEmail)")
print("Admin: \(isAdmin)")
print("Name Length: \(displayName.count) chars")

let poem = """
Roses are red,
Violets are blue,
Swift is awesome,
And so are you!
"""
print(poem)

let indented = """
    Line 1
    Line 2
    """
// 每行前面的 4 个空格会被去掉

let ch: Character = "A"
let emoji: Character = ""
// 遍历字符串中的每个字符
let greeting = "Hi!"
for char in greeting {
    print(char)
}
// 输出：H  i  !

// ============================================
// 生成格式化的产品说明
// 演示多行字符串和 Character 遍历
// ============================================
let productName = "Swift Pro"
let version = "2.0"
let features = ["Fast", "Safe", "Modern", "Open Source"]
// 使用多行字符串构建产品介绍
let description = """
Product: \(productName)
Version: \(version)
Features:
  - \(features[0])
  - \(features[1])
  - \(features[2])
  - \(features[3])
"""
print(description)
// 遍历产品名中的每个字符
print("Product name characters:")
for ch in productName {
    print("[\(ch)]", terminator: " ")
}
print()

// ============================================
// 客户邮件生成器
// 功能：字符串拼接、插值、多行、方法
// ============================================
import Foundation
// 1. 客户数据
let customerName = "Charlie Brown"
let projectName = "DataSync Pro"
let dueDate = "2026-08-15"
let amount = 2499.00
// 2. 邮件主题
let subject = "Invoice for \(projectName) - Due \(dueDate)"
print("Subject: \(subject)")
print(String(repeating: "=", count: subject.count + 10))
// 3. 邮件正文（多行字符串 + 插值）
let body = """
Dear \(customerName),
Thank you for choosing \(projectName).
Invoice Summary:
  - Project: \(projectName)
  - Amount: $\(String(format: "%.2f", amount))
  - Due Date: \(dueDate)
Please make the payment by \(dueDate).
If you have any questions, feel free to reply.
Best regards,
Swift Tech Team
"""
print(body)
// 4. 邮件验证
let isValidSubject = subject.hasPrefix("Invoice")
let containsProjectName = body.contains(projectName)
let isFormatted = body.hasSuffix("Team\n")
print("=== Validation ===")
print("Valid Subject: \(isValidSubject)")
print("Contains Project: \(containsProjectName)")
print("Proper Formatting: \(isFormatted)")
print("Body Length: \(body.count) chars")