@instance_variable在红宝石块内不可用? [英] @instance_variable not available inside a ruby block?

问题描述

使用以下代码:

def index
  @q = ""
  @q = params[:search][:q] if params[:search]
  q = @q
  @search = Sunspot.search(User) do
    keywords q
  end
  @users = @search.results
end

如果使用@q而不是q，则搜索始终返回空查询(")的结果.为什么是这样? @q变量对do ... end块不可用吗?

If @q is used instead of q, the search always returns results for an empty query (""). Why is this? Is the @q variable unavailable to the do...end block?

推荐答案

这取决于如何调用该块.如果使用yield关键字或Proc#call方法调用它，则可以在块中使用实例变量.如果使用Object#instance_eval或Module#class_eval调用它，则块的上下文将被更改，并且您将无法访问实例变量.

It depends on how the block is being called. If it is called using the yield keyword or the Proc#call method, then you'll be able to use your instance variables in the block. If it's called using Object#instance_eval or Module#class_eval then the context of the block will be changed and you won't be able to access your instance variables.

@x = "Outside the class"

class Test
  def initialize
    @x = "Inside the class"
  end

  def a(&block)
    block.call
  end

  def b(&block)
    self.instance_eval(&block)
  end
end

Test.new.a { @x } #=> "Outside the class"
Test.new.b { @x } #=> "Inside the class"

在您的情况下，看来Sunspot.search正在使用instance_eval在不同的上下文中调用您的块，因为该块需要轻松访问该keywords方法.

In your case, it looks like Sunspot.search is calling your block in a different context using instance_eval, because the block needs easy access to that keywords method.

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