为什么邮件块看不到我的变量?

问题描述

我是 Ruby 的新手，想知道为什么在这种情况下使用简单的 Sinatra 应用程序中的邮件"gem 会出现错误:

I'm new to Ruby and wondering why I am getting an error in this situation using the 'mail' gem in a simple Sinatra app:

post "/email/send" do

  @recipient = params[:email]

  Mail.deliver do
    to @recipient # throws error as this is undefined
    from '[e-mail]'
    subject 'testing sendmail'
    body 'testing sendmail'
  end

  erb :email_sent

end

然而这工作正常:

post "/email/send" do

  Mail.deliver do
    to '[e-mail]'
    from '[e-mail]'
    subject 'testing sendmail'
    body 'testing sendmail'
  end

  erb :email_sent

end

我怀疑这与块作用域和我对它的误解有关.

I suspect this is something to do with block scope and my misunderstanding of it.

推荐答案

正如 Julik 所说，Mail#delivery 使用 #instance_exec 执行你的块，它只是改变了 self 在运行块时(否则您将无法在块内调用方法 #to 和 #from).

As Julik says, Mail#delivery executes your block using #instance_exec, which simply changes self while running a block (you wouldn't be able to call methods #to and #from inside the block otherwise).

在这里你真正能做的是利用一个事实，即块是闭包.这意味着它记住"了它周围的所有局部变量.

What you really can do here is to use a fact that blocks are closures. Which means that it "remembers" all the local variables around it.

recipient = params[:email]
Mail.deliver do
    to recipient # 'recipient' is a local variable, not a method, not an instance variable
...
end

再次简单地说:

• 实例变量和方法调用依赖于self
• #instance_exec 改变self；
• 局部变量不依赖于self并且被块记住，因为块是闭包.

• instance variables and method calls depend on self
• #instance_exec changes the self;
• local variables don't depend on self and are remembered by blocks because blocks are closures.

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