在字符串和类名之间进行转换

发布于 2024-08-05 16:12:08 字数 152 浏览 2 评论 0原文

我有一个字符串，其中包含类名。例如，它是包含“Article”的字符串。该字符串来自 params[]。我应该怎么做才能像类名一样使用这个字符串？比如我想做：

Article.all

等等。

有什么想法吗？

原文

I have a string, containing an Class name. It is, for example, a string containing "Article". That string came up from the params[]. What should I do to work with this string as if it was a class name? For instance, I want to do:

Article.all

and so on.

Any idea?

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浅笑轻吟梦一曲 2024-08-12 16:12:08

此解决方案比 eval 更好，因为您正在评估可能被用户操纵并可能包含有害操作的 params 哈希值。作为一般规则：永远不要直接评估用户输入，这是一个很大的安全漏洞。

# Monkey patch for String class
    class String
      def to_class
        klass = Kernel.const_get(self)
        klass.is_a?(Class) ? klass : nil
      rescue NameError
        nil
      end
    end

# Examples
"Fixnum".to_class #=> Fixnum
"Something".to_class #=> nil

更新 - 与命名空间一起使用的更好版本：

 # Monkey patch for String class
    class String
      def to_class
        chain = self.split "::"
        klass = Kernel
        chain.each do |klass_string|
          klass = klass.const_get klass_string
        end
        klass.is_a?(Class) ? klass : nil
      rescue NameError
        nil
      end
    end

This solution is better than eval as you are evaluating params hash that might be manipulated by the user and could contain harmful actions. As a general rule: Never evaluate user input directly, that's a big security hole.

# Monkey patch for String class
    class String
      def to_class
        klass = Kernel.const_get(self)
        klass.is_a?(Class) ? klass : nil
      rescue NameError
        nil
      end
    end

# Examples
"Fixnum".to_class #=> Fixnum
"Something".to_class #=> nil

Update - a better version that works with namespaces:

 # Monkey patch for String class
    class String
      def to_class
        chain = self.split "::"
        klass = Kernel
        chain.each do |klass_string|
          klass = klass.const_get klass_string
        end
        klass.is_a?(Class) ? klass : nil
      rescue NameError
        nil
      end
    end

回复收藏 0 原文

空心↖ 2024-08-12 16:12:08

class Abc
end #=> nil
klass = eval("Abc") #=> Abc
klass.new #=> #<Abc:0x37643e8>

假设确实存在一个提供名称的类...

在 ActiveSupport 中，有 String#constantize，它做了同样的事情，但我相信它在 2.1 之后已被弃用。

编辑：这是 ActiveSupport 2.1.2 中的 Constantize 实现：

  def constantize(camel_cased_word)
    names = camel_cased_word.split('::')
    names.shift if names.empty? || names.first.empty?

    constant = Object
    names.each do |name|
      constant = constant.const_defined?(name) ? constant.const_get(name) : constant.const_missing(name)
    end
    constant
  end

class Abc
end #=> nil
klass = eval("Abc") #=> Abc
klass.new #=> #<Abc:0x37643e8>

Assumes there really is a class with the name provided...

In ActiveSupport, there was String#constantize, which did the same thing, but I believe it's deprecated after 2.1.

EDIT: this is the implementation of constantize from ActiveSupport 2.1.2:

  def constantize(camel_cased_word)
    names = camel_cased_word.split('::')
    names.shift if names.empty? || names.first.empty?

    constant = Object
    names.each do |name|
      constant = constant.const_defined?(name) ? constant.const_get(name) : constant.const_missing(name)
    end
    constant
  end

回复收藏 0 原文

羅雙樹 2024-08-12 16:12:08

我不确定我是否正确理解了你的意图。这里我假设 all 是 Article 的类方法，并且 all 返回一个文章数组。

class Article
    def self.all
       ["Peopleware" , "The Mythical Man-Month"]
    end

end

s = "Article"
all_of_article = []
eval("all_of_article = #{s + ".all"}")
puts all_of_article.inspect  # ["Peopleware", "The Mythical Man-Month"]

I am not sure whether I understand your intention correctly. Here I assume all is an Class method of Article and all return an array of articles.

class Article
    def self.all
       ["Peopleware" , "The Mythical Man-Month"]
    end

end

s = "Article"
all_of_article = []
eval("all_of_article = #{s + ".all"}")
puts all_of_article.inspect  # ["Peopleware", "The Mythical Man-Month"]

回复收藏 0 原文

~没有更多了~