Question

假设我有一个班级Article，这样：

class Article

  attr_accessor :title, :author

  def initialize(title, author)
    @title = title
    @author= author
  end

end

此外，变量atrib是包含属性名称的String。如何将此字符串转换为变量以用作吸气剂？

a = Article.new
atrib='title'
puts a.eval(atrib)     # <---- I want to do this

扩展

假设我现在有Array篇文章，我想按标题对它们进行排序。有没有办法使用&执行紧凑版本，如：

col = Article[0..10]
sorted_one = col.sort_by{|a| a.try('title') }   #This works
sorted_two = col.sort_by(&:try('title'))   #This does not work

Answer 1

您可以使用send或instance_variable_get：

a = Article.new 'Asdf', 'Coco'
a.send(:title) # Tries to call method named 'title'. Can raise NoMethodError
=> "Asdf"
a.instance_variable_get :@title # Looks for an instance variable, returns nil if one doesn't exist
=> "Asdf"
# If at rails like your case:
a.try :title # "Tries" to call 'title' method, returns nil if the receiver, `a` in this case, is nil
=> "Asdf"

回答你的扩展问题：不。 proc的&:symbol快捷方式依赖于Symbol#to_proc方法。因此，要启用该行为，您需要在Symbol类上重新设置该方法，顺便说一下，这是我一直关注的功能，所以......：

class Symbol
  def to_proc  
    ->(x) { x.instance_eval(self.to_s) }    
  end  
end

[1,2,3].map(&:"to_s.to_i * 10")
=> [10, 20, 30]

Answer 2

ActiveRecord个实例有一个attributes哈希：

a = Article.new(title: 'foo')
#=> <#Article id: nil, title: "foo">

atrib = 'title'
a.attributes[atrib]
#=> "foo"

您可以使用order从数据库中获取已排序的对象：

Article.order('title').first(10)
#=> array of first 10 articles ordered by title

Ruby / Rails将字符串转换为类属性

2 个答案: