Ruby 中方法参数的思考 [英] Reflection on method parameters in Ruby

问题描述

参加以下课程:

class Automator
  def fill_specific_form(fields)
    fields.each_pair do |key, value|
      puts "Setting '#{key}' to '#{value}'"
    end
  end
end

a = Automator.new
a.fill_specific_form :first_name => "Mads", :last_name => "Mobæk"

# => Setting 'first_name' to 'Mads'
# => Setting 'last_name' to 'Mobæk'

是否可以在没有散列的情况下做同样的事情?由于所有参数都是必需的，我想要一个具有以下签名的方法:

Is it possible to do the same without a hash? Since all parameters are required, I want a method with the following signature:

fill_specific_form(first_name, last_name)

在我看来，这可以通过让方法体反射和迭代其参数来实现，从而实现相同的结果.

In my mind this would be possible by having the method body reflect and iterate over its parameters, thus achieving the same result.

您将如何实现这一点?是否已经存在这种模式/习语?两个明显的好处是 IDE 中的参数信息，并且不必检查是否提供了所有散列键.

How would you implement this? Does a pattern/idiom for this exist already? Two obvious benefits would be parameter information in IDEs and not having to check if all hash keys are supplied.

我想避免的是:

puts "Setting first_name to #{first_name}"
puts "Setting last_name to #{last_name}"
# and so on

推荐答案

如果你没有在方法内部设置其他局部变量，local_variables 会给你一个方法参数名称的列表(如果你设置了设置其他变量，您可以首先调用 local_variables 并记住结果).所以你可以用 local_variables+eval 做你想做的事:

If you set no other local variables inside the method, local_variables will give you a list of the method's parameter names (if you do set other variables you can just call local_variables first thing and remember the result). So you can do what you want with local_variables+eval:

class Automator
  def fill_specific_form(first_name, last_name)
    local_variables.each do |var|
      puts "Setting #{var} to #{eval var.to_s}"
    end
  end
end

Automator.new().fill_specific_form("Mads", "Mobaek")

但是请注意，这是纯粹的邪恶.

Be however advised that this is pure evil.

至少对于你的例子

puts "Setting first_name to #{first_name}"
puts "Setting last_name to #{last_name}"

似乎更明智.

你也可以做 fields = {:first_name =>名字, :last_name =>last_name} 在方法的开头，然后使用您的 fields.each_pair 代码.

You could also do fields = {:first_name => first_name, :last_name => last_name} at the beginning of the method and then go with your fields.each_pair code.

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