判断祖先是Ruby中的类还是模块的方法？

Posted 2023-02-19

【中文标题】判断祖先是Ruby中的类还是模块的方法？

【英文标题】：Method to tell if ancestor is a Class or Module in Ruby?

【发布时间】：2011-04-11 05:19:57

【问题描述】：

如果我有一个像下面这样的类，我如何判断祖先是类还是模块？

ActiveRecord::Base.send(:include, SomeLibrary)

class Group < ActiveRecord::Base
  include SomeLibrary::Core
end

class SubGroup < Group

end

ancestor_names = SubGroup.ancestors.map(&:name)
puts ancestor_names.inspect
  #=> [
  "SubGroup", "SomeLibrary::Core::InstanceMethods", "SomeLibrary::Core", 
  "Group", "ActiveRecord::Base", "SomeLibrary", "ActiveRecord::Aggregations", 
  "ActiveRecord::Transactions", "ActiveRecord::Reflection", "ActiveRecord::Batches", 
  "ActiveRecord::Calculations", "ActiveRecord::Serialization", "ActiveRecord::AutosaveAssociation", 
  "ActiveRecord::NestedAttributes", "ActiveRecord::Associations", "ActiveRecord::AssociationPreload", 
  "ActiveRecord::NamedScope", "ActiveRecord::Callbacks", "ActiveRecord::Observing", 
  "ActiveRecord::Timestamp", "ActiveRecord::Dirty", "ActiveRecord::AttributeMethods", 
  "ActiveRecord::Locking::Optimistic", "ActiveRecord::Locking::Pessimistic", 
  "ActiveSupport::Callbacks", "ActiveRecord::Validations", "Object", "Mocha::ObjectMethods", 
  "JSON::Pure::Generator::GeneratorMethods::Object", "ActiveSupport::Dependencies::Loadable", 
  "Base64::Deprecated", "Base64", "PP::ObjectMixin", "Kernel"
]

我希望能够做这样的事情：

ancestor_names.each do |name|
  if class?(name)
    puts "#name is a Class"
  elsif module?(name)
    puts "#name is a Module"
  end
end

或者...

SubGroup.ancestor_classes #=> only the classes in the tree
SubGroup.ancestor_modules #=> only the modules in the tree

归结为，如何检查对象是类还是模块？

【参考方案1】：

嗯，这就是 included_modules 的用途，所以您可能正在寻找的是：

SubGroup.included_modules                       #=> module ancestors
SubGroup.ancestors - SubGroup.included_modules  #=> class ancestors

或者，使用辅助方法：

class Class
  def ancestor_classes
    ancestors - included_modules
  end
end

SubGroup.included_modules  #=> module ancestors
SubGroup.ancestor_classes  #=> class ancestors

【参考方案2】：

使用Object#instance_of?:

Object.instance_of? Class  # => true
Object.instance_of? Module # => false
Kernel.instance_of? Class  # => false
Kernel.instance_of? Module # => true

【参考方案3】：

以上答案已经足够了。下面的内容也可能会有所帮助。

pp SubGroup.ancestors.map |c| c.instance_of?(Class) ? "CLASS: #c" : "MODULE: #c"