在ruby中从自身获取实例变量名称 [英] get instance variable name from itself in ruby

问题描述

我有一个实例变量@foo，我想写一些代码，以便得到字符串'foo'

I have an instance variable @foo and I want to write some code so that I get string 'foo'

有任何提示吗?

推荐答案

如果所拥有的只是对对象的引用，则不能真正做到干净.

If all you have is a reference to the object, you can't really do it cleanly.

def foo
  bar @something
end

def bar(value)
  value # no clean way to know this is @something
end

---

我唯一想到的办法是遍历self上的所有实例变量，寻找匹配项.但这是一个非常混乱的方法，可能会很慢.

---

The only hack I can think of is to loop through ALL instance variables on self, looking for matches. But its a very messy approach that's likely to be slow.

def bar(value)
  instance_variables.each do |ivar_name|
    if instance_variable_get(ivar_name) == value
      return ivar_name.to_s.sub(/^@/, '') # change '@something' to 'something'
    end
  end

  # return nil if no match was found
  nil 
end

@something = 'abc123'
bar @something # returns 'something'

# But passing the same value, will return a value it's equal to as well
bar 'abc123' # returns 'something'

之所以可行，是因为instance_variables返回的符号数组是实例变量的名称.

This works because instance_variables returns an array of symbols that are the names of instance variables.

instance_variables
#=> [:@something, :@whatever] 

instance_variable_get和instance_variable_get允许您通过名称获取值.

And instance_variable_get allows you to fetch the value by it's name.

instance_variable_get :@something # note the @
#=> 'abc123'

结合使用这两种方法，您可以接近所需的内容.

Combine the two methods and you can get close to what you want.

明智地使用它.在使用基于此的解决方案之前，请先查看是否可以以某种方式重构事物，以使其不必要.元编程就像武术一样.您应该知道它是如何工作的，但是要有纪律避免在可能的情况下使用它.

Just use it wisely. Before using a solution based on this, see if you can refactor things a way so that it's not necessary. Meta-programming is like a martial art. You should know how it works, but have the discipline to avoid using it whenever possible.

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