# 在大多数语言中，数字是基本类型
# 在 Ruby 中，数字也是对象
42.class          # => Integer
42.even?          # => true
42.times { |i| puts i }  # 输出 0 到 41

# 字符串是对象
"hello".upcase    # => "HELLO"
"hello".length    # => 5

# nil 也是对象
nil.class         # => NilClass
nil.nil?          # => true
nil.to_s          # => ""

# 布尔值也是对象
true.class        # => TrueClass
false.class       # => FalseClass

# 类本身也是对象
String.class      # => Class
Class.class       # => Class

# Ruby 尽量让代码的行为符合你的直觉
# 例：字符串是可变的（不像 Python 的字符串不可变）
s = "hello"
s << " world"  # 原地修改
puts s          # => "hello world"

# 例：数组下标越界不会报错，返回 nil
arr = [1, 2, 3]
arr[10]         # => nil（而非 IndexError）

# 例：块（Block）的引入让迭代变得自然
[1, 2, 3].each do |n|
  puts n * 2
end

# Ruby 风格：简洁、表达力强
# 过滤偶数并求平方
(1..10).select(&:even?).map { |n| n**2 }
# => [4, 16, 36, 64, 100]

# 等价的 Python 风格
# [n**2 for n in range(1, 11) if n % 2 == 0]

# 等价的 JavaScript 风格
# Array.from({length: 10}, (_, i) => i + 1).filter(n => n % 2 === 0).map(n => n ** 2)

# 查看当前 Ruby 版本和实现
puts RUBY_VERSION    # => "3.3.0"
puts RUBY_ENGINE     # => "ruby" (MRI), "jruby", "truffleruby" 等
puts RUBY_PLATFORM   # => "x86_64-linux"

# 这些公司/项目都在使用 Ruby
ruby_users = {
  "GitHub"        => "代码托管平台，Rails 架构",
  "Shopify"       => "电商平台，全球最大的 Rails 应用之一",
  "Basecamp"      => "项目管理工具，Rails 的诞生地",
  "Airbnb"        => "短租平台，早期使用 Rails",
  "Stripe"        => "支付平台，Ruby API",
  "Twitch"        => "直播平台，Ruby 微服务",
  "Hulu"          => "流媒体，Ruby 后端",
  "Cookpad"       => "食谱分享，日本 Ruby 社区重要成员",
  "Discourse"     => "论坛系统，Rails 构建"
}

# Ruby 社区的重要活动
events = [
  { name: "RubyConf",          location: "美国",  type: "国际大会" },
  { name: "RailsConf",         location: "美国",  type: "Rails 专题" },
  { name: "RubyKaigi",         location: "日本",  type: "国际大会" },
  { name: "Euruko",            location: "欧洲",  type: "欧洲大会" },
  { name: "RubyConf China",    location: "中国",  type: "中国大会" },
  { name: "RubyKaigi Takeout", location: "线上",  type: "线上会议" }
]

events.each do |event|
  puts "#{event[:name]} (#{event[:location]}) - #{event[:type]}"
end

# Ruby：块和迭代器
[1, 2, 3].each do |n|
  puts n if n.even?
end

# Python
# for n in [1, 2, 3]:
#     if n % 2 == 0:
#         print(n)

# JavaScript
# [1, 2, 3].forEach(n => { if (n % 2 === 0) console.log(n) })

# Ruby 的块让代码更接近自然语言
5.times { puts "Hello!" }
3.times do
  puts "Ruby is fun!"
end

# greeting.rb - 一个简单的问候程序

class Greeter
  attr_reader :name

  def initialize(name = "World")
    @name = name
  end

  def greet
    case Time.now.hour
    when 5..11
      "早上好，#{@name}！☀️"
    when 12..13
      "中午好，#{@name}！🌞"
    when 14..17
      "下午好，#{@name}！🌤️"
    when 18..21
      "晚上好，#{@name}！🌙"
    else
      "夜深了，#{@name}，早点休息！💤"
    end
  end
end

# 使用
greeter = Greeter.new("Ruby 学习者")
puts greeter.greet

ruby greeting.rb

# IRB 实验
"Ruby".reverse           # => "ybuR"
(1..100).sum             # => 5050
"hello world".split      # => ["hello", "world"]
[3, 1, 4, 1, 5].sort     # => [1, 1, 3, 4, 5]
[3, 1, 4, 1, 5].uniq     # => [3, 1, 4, 5]
"ruby".chars.shuffle.join # => 随机排列