Ruby

# 变量（无需声明类型）
name = "Alice"
age = 30
pi = 3.14159
is_valid = true

# 常量（首字母大写）
MAX_SIZE = 100
PI = 3.14159

# 符号（Symbol）- 不可变的字符串
status = :active
direction = :north

# 数组
numbers = [1, 2, 3, 4, 5]
mixed = [1, "two", 3.0, :four]

# 哈希（Hash）
person = { name: "Bob", age: 25, city: "NYC" }
legacy_hash = { "name" => "Charlie", "age" => 35 }

# 范围（Range）
range1 = 1..10      # 1 到 10（包含10）
range2 = 1...10     # 1 到 10（不包含10）

# if/elsif/else
age = 18
if age >= 18
  puts "Adult"
elsif age >= 13
  puts "Teenager"
else
  puts "Child"
end

# 单行 if
puts "Adult" if age >= 18

# unless（if 的反向）
puts "Not adult" unless age >= 18

# case/when
grade = 'B'
case grade
when 'A'
  puts "Excellent"
when 'B'
  puts "Good"
when 'C'
  puts "Average"
else
  puts "Need improvement"
end

# 三元运算符
result = age >= 18 ? "Adult" : "Minor"

# while 循环
i = 0
while i < 5
  puts i
  i += 1
end

# until 循环（while 的反向）
i = 0
until i >= 5
  puts i
  i += 1
end

# for 循环
for i in 0..4
  puts i
end

# times 循环
5.times do |i|
  puts i
end

# each 遍历数组
[1, 2, 3].each do |num|
  puts num
end

# each 遍历哈希
person.each do |key, value|
  puts "#{key}: #{value}"
end

# loop 无限循环
loop do
  puts "Infinite loop"
  break if some_condition
end

# 定义类
class Person
  # 类变量
  @@count = 0

  # 属性访问器
  attr_accessor :name, :age    # 读写
  attr_reader :id              # 只读
  attr_writer :password        # 只写

  # 初始化方法（构造函数）
  def initialize(name, age)
    @name = name      # 实例变量
    @age = age
    @id = @@count += 1
  end

  # 实例方法
  def introduce
    "Hi, I'm #{@name}, #{@age} years old."
  end

  # 类方法
  def self.total_count
    @@count
  end

  # 私有方法
  private

  def secret_method
    "This is private"
  end
end

# 创建对象
person = Person.new("Alice", 30)
puts person.introduce
puts person.name
person.age = 31
puts Person.total_count

# 父类
class Animal
  attr_accessor :name

  def initialize(name)
    @name = name
  end

  def speak
    "Some sound"
  end
end

# 子类继承
class Dog < Animal
  def speak
    "Woof!"
  end

  def fetch
    "#{@name} is fetching the ball"
  end
end

# 使用 super 调用父类方法
class Cat < Animal
  def initialize(name, color)
    super(name)  # 调用父类的 initialize
    @color = color
  end

  def speak
    "Meow!"
  end
end

dog = Dog.new("Buddy")
puts dog.speak      # "Woof!"
puts dog.fetch      # "Buddy is fetching the ball"

# 模块用于命名空间和混入（Mixin）
module Swimmable
  def swim
    "Swimming..."
  end
end

module Flyable
  def fly
    "Flying..."
  end
end

# 混入模块
class Duck
  include Swimmable
  include Flyable

  def quack
    "Quack!"
  end
end

duck = Duck.new
puts duck.swim   # "Swimming..."
puts duck.fly    # "Flying..."
puts duck.quack  # "Quack!"

# 命名空间
module MyApp
  module Models
    class User
      # User model
    end
  end
end

user = MyApp::Models::User.new

# 基本方法
def greet(name)
  "Hello, #{name}!"
end

# 默认参数
def greet(name = "Guest")
  "Hello, #{name}!"
end

# 可变参数
def sum(*numbers)
  numbers.reduce(0, :+)
end
puts sum(1, 2, 3, 4)  # 10

# 关键字参数
def create_user(name:, age:, email: nil)
  { name: name, age: age, email: email }
end
create_user(name: "Alice", age: 30)

# 隐式返回（最后一行表达式）
def add(a, b)
  a + b  # 自动返回
end

# 块（Block）
[1, 2, 3].each { |n| puts n }

[1, 2, 3].each do |n|
  puts n * 2
end

# 自定义方法接受块
def my_method
  yield if block_given?
end
my_method { puts "Block executed" }

# Proc（可存储的块）
my_proc = Proc.new { |x| x * 2 }
puts my_proc.call(5)  # 10

# Lambda（更严格的 Proc）
my_lambda = lambda { |x| x * 2 }
my_lambda = ->(x) { x * 2 }  # 简写
puts my_lambda.call(5)  # 10

# Lambda 和 Proc 的区别
# 1. Lambda 检查参数数量，Proc 不检查
# 2. Lambda 的 return 只退出 lambda，Proc 的 return 退出包含它的方法

arr = [1, 2, 3, 4, 5]

# 遍历和转换
arr.map { |x| x * 2 }        # [2, 4, 6, 8, 10]
arr.select { |x| x > 2 }     # [3, 4, 5]
arr.reject { |x| x > 2 }     # [1, 2]
arr.find { |x| x > 2 }       # 3
arr.reduce(0) { |sum, x| sum + x }  # 15

# 其他常用方法
arr.first       # 1
arr.last        # 5
arr.length      # 5
arr.empty?      # false
arr.include?(3) # true
arr.reverse     # [5, 4, 3, 2, 1]
arr.sort        # [1, 2, 3, 4, 5]
arr.uniq        # 去重

str = "Hello World"

str.upcase          # "HELLO WORLD"
str.downcase        # "hello world"
str.capitalize      # "Hello world"
str.reverse         # "dlroW olleH"
str.length          # 11
str.split           # ["Hello", "World"]
str.include?("World")  # true
str.gsub("World", "Ruby")  # "Hello Ruby"

# 字符串插值
name = "Alice"
"Hello, #{name}!"   # "Hello, Alice!"

# 多行字符串
text = <<~HEREDOC
  This is a
  multi-line string
  with indentation removed
HEREDOC

hash = { a: 1, b: 2, c: 3 }

hash.keys           # [:a, :b, :c]
hash.values         # [1, 2, 3]
hash.has_key?(:a)   # true
hash.merge({ d: 4 })  # { a: 1, b: 2, c: 3, d: 4 }
hash.select { |k, v| v > 1 }  # { b: 2, c: 3 }

# 基本异常处理
begin
  # 可能抛出异常的代码
  result = 10 / 0
rescue ZeroDivisionError => e
  puts "Error: #{e.message}"
rescue StandardError => e
  puts "Other error: #{e.message}"
else
  puts "No errors"
ensure
  puts "Always executed"
end

# 抛出异常
def validate_age(age)
  raise ArgumentError, "Age must be positive" if age < 0
end

# 自定义异常
class CustomError < StandardError; end

begin
  raise CustomError, "Something went wrong"
rescue CustomError => e
  puts e.message
end

# 读取文件
content = File.read("file.txt")

# 逐行读取
File.readlines("file.txt").each do |line|
  puts line
end

# 写入文件
File.write("file.txt", "Hello, Ruby!")

# 使用块自动关闭文件
File.open("file.txt", "w") do |file|
  file.puts "Line 1"
  file.puts "Line 2"
end

# 追加内容
File.open("file.txt", "a") do |file|
  file.puts "Appended line"
end

# 检查文件存在
File.exist?("file.txt")
File.directory?("path/to/dir")

# 局部变量
name = "Ruby"

# 实例变量
@instance_var = "instance"

# 类变量
@@class_var = "class"

# 全局变量
$global_var = "global"

# 常量
CONSTANT = "immutable"

# 符号（不可变字符串）
status = :active

# 数组操作链
result = [1, 2, 3, 4, 5]
  .map { |x| x * 2 }
  .select { |x| x > 5 }
  .reduce(:+)
# result = 18

# 哈希操作
person = { name: "Alice", age: 30 }
person.merge!(city: "NYC")
person.transform_values { |v| v.to_s }

class BankAccount
  attr_reader :balance

  def initialize(initial_balance = 0)
    @balance = initial_balance
  end

  def deposit(amount)
    @balance += amount if amount > 0
  end

  def withdraw(amount)
    @balance -= amount if amount > 0 && amount <= @balance
  end
end

account = BankAccount.new(1000)
account.deposit(500)
account.withdraw(200)

module Logging
  def log(message)
    puts "[#{Time.now}] #{message}"
  end
end

class Application
  include Logging

  def run
    log "Application started"
  end
end

# 各种迭代方式
5.times { |i| puts i }
1.upto(5) { |i| puts i }
5.downto(1) { |i| puts i }

# 自定义迭代器
class MyCollection
  def initialize(data)
    @data = data
  end

  def each
    @data.each { |item| yield item }
  end
end

collection = MyCollection.new([1, 2, 3])
collection.each { |item| puts item }