初次上手Elixir的原子（Atom），详解模式匹配、函数参数标识、状态机等典型场景的实现方案

# 验证原子内存特性
a = :apple
b = :apple
IO.puts(a == b)  # 输出true
IO.puts(:apple == :apple)  # 输出true

defmodule ResponseHandler do
  # 处理不同响应状态的函数分派
  def process({:ok, data}), do: "成功获取#{inspect(data)}"
  def process({:error, :timeout}), do: "请求超时"
  def process({:error, :not_found}), do: "资源不存在"
  
  # 带原子参数的函数重载
  def connect(:tcp, port), do: "建立TCP连接#{port}"
  def connect(:udp, port), do: "建立UDP连接#{port}"
end

# 测试用例
ResponseHandler.process({:ok, %{id: 1}}) |> IO.puts()  # 输出"成功获取%{id: 1}"
ResponseHandler.connect(:udp, 8080) |> IO.puts()       # 输出"建立UDP连接8080"

defmodule UserRepo do
  # 使用原子标识操作类型
  def operate(:create, params) do
    %User{}
    |> User.changeset(params)
    |> Repo.insert()
  end

  def operate(:update, %User{} = user, params) do
    user
    |> User.changeset(params)
    |> Repo.update()
  end
end

# 创建用户示例
UserRepo.operate(:create, %{name: "张三", age: 25})

# 更新用户示例
user = Repo.get(User, 1)
UserRepo.operate(:update, user, %{age: 26})

defmodule TrafficLight do
  # 状态转移表
  @transition %{
    red: :green,
    green: :yellow,
    yellow: :red
  }

  def change(current) do
    next = @transition[current]
    case next do
      nil -> {:error, :invalid_state}
      state -> {:ok, state}
    end
  end
end

# 状态转换测试
TrafficLight.change(:red)    # => {:ok, :green}
TrafficLight.change(:black)  # => {:error, :invalid_state}

# 安全的状态转换验证
defmodule SafeState do
  @valid_states [:idle, :running, :paused]
  
  def change(current, next) when next in @valid_states do
    # 安全的状态转换逻辑
  end
end

# 安全转换示例
"running" |> String.to_existing_atom()  # 推荐方式
:running |> Atom.to_string()            # 输出"running"