Ruby - 实际上获取实例的所有方法

Question

在这个问题中:

How to list all methods for an object in Ruby?

您可以调用foo.methods并获取所有方法。但这并不能获取所有方法。 Rails 中的示例，使用 ActiveStorage:

Image.first.specimens.first.methods.include?(:variant)
# => false
Image.first.specimens.first.respond_to?(:variant)
# => true
Image.first.specimens.first.variant
Traceback (most recent call last):
        1: from (irb):3
ArgumentError (wrong number of arguments (given 0, expected 1))
Image.first.specimens.first.method(:variant)
# => #<Method: ActiveStorage::Attachment(id: integer, name: string, record_type: string, record_id: integer, blob_id: integer, created_at: datetime)#variant>

鉴于正在引发 ArgumentError，它respond_to？，并且我可以获取该方法，它确实具有变体方法。但它没有用 .methods 显示。我如何查看完整的方法列表？

Answer 1

也许您错过了链接帖子 How to list all methods for an object in Ruby? 已接受答案中的最后一段:

Added Note that :has_many does not add methods directly. Instead, the ActiveRecord machinery uses the Ruby method_missing and responds_to techniques to handle method calls on the fly. As a result, the methods are not listed in the methods method result.

为了更清楚地说明发生了什么，代码示例:

class Foo
  def hello
    puts 'Hello'
  end

  def method_missing(name, *args, &block)
    case name
      when :unknown_method
        puts "handle unknown method %s" % name # name is a symbol
      else
        super #raises NoMethodError unless there is something else defined
    end
  end
end

foo = Foo.new
p foo.respond_to?(:hello) #-> true
p foo.respond_to?(:unknown_method) #-> false
foo.unknown_method  #-> 'handle unknown method unknown_method'
foo.another_unknown_method  #-> Exception

方法unknown_method从未定义，但有一个方法可以处理未知方法。因此，该类给人的印象是存在一个方法，但实际上并没有。

也许How can I get source code of a method dynamically and also which file is this method locate in帮助获取有关内容的信息:

Foo.instance_method(:method_missing).source_location

添加

当您定义自己的 method_missing 时，您还应该将 respond_to_missing? 的行为更改为 respond_to_missing?

  def respond_to_missing?(method, *)
    return method == :unknown_method || super
    #or if you have a list of methods:
    #~ return %i{unknown_method}.include?(method) || super
    #or with a regex for 
    #~ method =~ /another_(\w+)/ || super
  end
end

另请参阅`respond_to?` vs. `respond_to_missing?`了解详情。