Question

在默认模块之后包含偶数栏，它仍然无法覆盖Default.foo。这是一种方法吗？

module Default
  extend ActiveSupport::Concern
  included do
    define_singleton_method :foo do
      41
    end
  end
end
module Bar
  extend ActiveSupport::Concern
  module ClassMethods
    def foo
      42
    end
  end
end
class Foo
  include Default
  include Bar
end

Foo.foo
=> 41  #From Default.foo

Answer 1

如果我们在您的代码中添加一些调试语句，我们将看到定义和包含模块的顺序如下所示：

Default

由于在定义模块Bar之后发生了包含模块foo的事件，因此有效的included的定义是定义的定义在模块Default的{{1}}块中。

添加了调试语句的代码

require "rails"

module Default
  extend ActiveSupport::Concern
  puts "Defined => Default"
  included do
    define_singleton_method :foo do
      41
    end
    puts "Included => Default"
  end
end
module Bar
  extend ActiveSupport::Concern
  puts "Defined => Bar"
  module ClassMethods
    puts "Defined => ClassMethods"
    def foo
      42
    end
  end
  included do
    puts "Included => Bar"
  end
end
class Foo
  include Default
  include Bar
end

p Foo.foo

如果您希望foo的{{1}}定义生效，那么您也可以在Bar included块中定义它，如图所示以下

Bar

以上程序的输出

require "rails" module Default extend ActiveSupport::Concern puts "Defined => Default" included do define_singleton_method :foo do 41 end puts "Included => Default" end end module Bar extend ActiveSupport::Concern puts "Defined => Bar" module ClassMethods puts "Defined => ClassMethods" def foo 42 end end included do puts "Included => Bar" define_singleton_method :foo do 42 end end end class Foo include Default include Bar end p Foo.foo

在`included`块vs`ClassMethods`中的Ruby`define_singleton_method`

1 个答案: