Elixir中的return语句 [英] Return statement in Elixir

问题描述

我需要一个具有某种逐步逻辑的功能，我想知道如何制作一个.让我们以网站上的登录过程为例，因此我需要以下逻辑:

I need a function with some kind of a step-by-step logic and I wonder how I can make one. Let's take a log in process on a site as an example, so I need the following logic:

1)电子邮件存在吗?是->继续；否->返回错误

1) Email is present? Yes -> Go on; No -> Return an error

2)电子邮件至少包含5个字符?是->继续；否->返回错误

2) Email has at least 5 characters? Yes -> Go on; No -> Return an error

3)密码存在吗?是->继续；否-返回错误

3) Password is present? Yes -> Go on; No - Return an error

依此类推...

要实现此目的，我通常会使用return语句，这样，如果不存在电子邮件，我会退出执行该函数，并使其返回错误.但是我在Elixir中找不到类似的东西，因此我需要一个建议.我现在看到的唯一方法是使用嵌套条件，但是也许有更好的方法?

And to implement this, I would usually use a return statement so that if the email is not present, I quit executing the function and make it return an error. But I can't find something similar to this in Elixir so I need an advice. The only way I can see now is to use nested conditions but maybe there is a better way?

推荐答案

这是一个有趣的问题，因为您需要执行多项检查，提早退出，并在此过程中转换某些状态(连接).我通常会按照以下方式处理此问题:

This is an interesting problem because you need to perform multiple checks, exit early, and in the process transform some state (connection). I typically approach this problem as follows:

• 我将每个检查实现为一个功能，该功能将state作为输入并返回{:ok, new_state}或{:error, reason}.
• 然后，我构建一个泛型函数，该函数将调用检查函数列表，如果所有检查都成功，则返回遇到的第一个{:error, reason}或{:ok, last_returned_state}.

• I implement each check as a function which takes state as an input and returns {:ok, new_state} or {:error, reason}.
• Then, I build a generic function that will invoke a list of check functions, and return either the first encountered {:error, reason} or {:ok, last_returned_state} if all checks succeeded.

让我们首先看看通用函数:

Let's see the generic function first:

defp perform_checks(state, []), do: {:ok, state}
defp perform_checks(state, [check_fun | remaining_checks]) do
  case check_fun.(state) do
    {:ok, new_state} -> perform_checks(new_state, remaining_checks)
    {:error, _} = error -> error
  end
end

现在，我们可以按以下方式使用它:

Now, we can use it as follows:

perform_checks(conn, [
  # validate mail presence
  fn(conn) -> if (...), do: {:error, "Invalid mail"}, else: {:ok, new_conn} end,

  # validate mail format
  fn(conn) -> if (...), do: {:error, "Invalid mail"}, else: {:ok, new_conn} end,

  ...
])
|> case do
  {:ok, state} -> do_something_with_state(...)
  {:error, reason} -> do_something_with_error(...)
end

或者将所有检查移至已命名的私有函数，然后执行以下操作:

Or alternatively move all checks to named private functions and then do:

perform_checks(conn, [
  &check_mail_presence/1,
  &check_mail_format/1,
  ...
])

您还可以研究 elixir-pipes ，这可能有助于您使用管道来表达这一点.

You could also look into the elixir-pipes which might help you express this with pipeline.

最后，在Phoenix/Plug的上下文中，您可以将检查声明为

Finally, in the context of Phoenix/Plug, you could declare your checks as a series of plugs and halt on first error.

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