Ruby-on-rails Rails：named_scope、lambda 和块

Rails: named_scope, lambda and blocks

提问by Gav

I thought the following two were equivalent:

我认为以下两个是等效的：

named_scope :admin, lambda { |company_id| {:conditions => ['company_id = ?', company_id]} }

named_scope :admin, lambda do |company_id| 
  {:conditions => ['company_id = ?', company_id]}
end

but Ruby is complaining:

但 Ruby 抱怨：

ArgumentError: tried to create Proc object without a block

Any ideas?

有任何想法吗？

回答by Martin DeMello

it's a parser problem. try this

这是一个解析器问题。尝试这个

named_scope :admin, (lambda do |company_id| 
  {:conditions => ['company_id = ?', company_id]}
end)

回答by Mike Woodhouse

I think the problem may be related to the difference in precedence between {...}and do...end

我认为问题可能与{...}和之间的优先级差异有关do...end

There's some SO discussion here

这里也有一些SO讨论这里

I think assigning a lambda to a variable (which would be a Proc) couldbe done with a do ... end:

我认为将 lambda 分配给一个变量（这将是一个 Proc）可以通过以下方式完成do ... end：

my_proc = lambda do 
  puts "did it"
end
my_proc.call #=> did it

回答by Kelvin

If you're on ruby 1.9 or later ¹, you can use the lambda literal (arrow syntax), which has high enough precedence to prevent the method call from "stealing" the block from the lambda.

如果您使用的是 ruby​​ 1.9 或更高版本¹，则可以使用 lambda 文字（箭头语法），它具有足够高的优先级以防止方法调用从 lambda 中“窃取”块。

named_scope :admin, ->(company_id) do 
  {:conditions => ['company_id = ?', company_id]}
end

---

---

^{1 The first stable Ruby 1.9.1 release was 2009-01-30.}

^{1 第一个稳定的 Ruby 1.9.1 版本是 2009-01-30。}

回答by khelll

It's something related to precedence as I can tell

据我所知，这与优先级有关

1.upto 3 do # No parentheses, block delimited with do/end
  |x| puts x 
end

1.upto 3 {|x| puts x } # Syntax Error: trying to pass a block to 3!