为什么Mail块看不到我的变量？

Question

我是Ruby的新手,想知道为什么我在这种情况下使用简单的Sinatra应用程序中的'mail'gem获得错误:

post "/email/send" do

  @recipient = params[:email]

  Mail.deliver do 
    to @recipient # throws error as this is undefined
    from 'server@domain.com'
    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 'me@domain.com'
    from 'server@domain.com'
    subject 'testing sendmail'
    body 'testing sendmail'
  end

  erb :email_sent

end

我怀疑这与块范围和我对它的误解有关.

Answer 1

正如Julik所说,使用Mail#delivery执行你的块#instance_exec,它只是self在运行一个块时更改(否则你将无法调用方法#to和#from块内).

你在这里真正可以做的是使用块是闭包的事实.这意味着它"记住"它周围的所有局部变量.

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

再简单地说:

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

Answer 2

如果您仔细阅读文档,Mail您将找到一个可行的替代解决方案.而不是使用:

Mail.deliver do 
  to @recipient # throws error as this is undefined
  from 'server@domain.com'
  subject 'testing sendmail'
  body 'testing sendmail'
end

你可以使用Mail的new()方法,传入参数,并忽略块:

Mail.new(
  to:      @recipient,
  from:    'server@domain.com',
  subject: 'testing sendmail',
  body:    'testing sendmail'
).deliver!

或备用哈希元素定义:

Mail.new(
  :to      => @recipient,
  :from    => 'server@domain.com',
  :subject => 'testing sendmail',
  :body    => 'testing sendmail'
).deliver!

在pry,或irb你会看到:

pry(main)> Mail.new(
pry(main)* to: 'me@domain.com',
pry(main)* from: 'me@' << `hostname`.strip,
pry(main)* subject: 'test mail gem',
pry(main)* body: 'this is only a test'
pry(main)* ).deliver!
=> #<Mail::Message:59273220, Multipart: false, Headers: <Date: Fri, 28 Oct 2011 09:01:14 -0700>, <From: me@myhost.domain.com>, <To: me@domain.com>, <Message-ID: <4eaad1cab65ce_579b2e8e6c42976d@myhost.domain.com>>, <Subject: test mail gem>, <Mime-Version: 1.0>, <Content-Type: text/plain>, <Content-Transfer-Encoding: 7bit>>

该new方法有几种可以使用的变体.这也来自文档,可能会更好:

作为旁注,您还可以通过直接创建Mail :: Message对象,然后通过字符串,符号或直接方法调用传递值来创建新电子邮件.有关更多信息,请参阅Mail :: Message.

 mail = Mail.new
 mail.to = 'mikel@test.lindsaar.net'
 mail[:from] = 'bob@test.lindsaar.net'
 mail['subject'] = 'This is an email'
 mail.body = 'This is the body'

接着是mail.deliver!.

另请注意,在前面的示例中,有多种方法可以访问邮件信封中的各种标头.这是一个灵活的宝石,似乎经过深思熟虑,很好地遵循Ruby方式.