Question

有没有办法获取实例方法并将其添加到类中（反之亦然）？

这是我的尝试，但它失败了，因为Ruby不让我将实例方法绑定到类：

#!/usr/bin/env ruby

SOMETHING = :a
class SomeClass
  def some_method(variable, value)
    case SOMETHING
    when :c
      "output for case C"
    when :a, :b
      "output for A or B"
    end
  end
  # here's my failed attampt to add some_method to SomeClass:
  self.instance_method(:some_method).bind(self)
end

# it works as an instance method
bash = SomeClass.new
puts bash.some_method("EDITOR","vim")

# but not as a class method... yet
puts SomeClass.some_method("EDITOR","vim")

错误是“bind参数必须是SomeClass的实例”。换句话说，我无法调用bind(self)，因为self 是类，而不是类的实例。

Answer 1

您可以使用此方法定义一个模块并include和extend您的课程：

使用include定义实例方法，使用extend定义类方法。

MWE：

SOMETHING = :a

module SomeClassMeth
  def some_method(variable, value)
    case SOMETHING
    when :c
      "output for case C"
    when :a, :b
      "output for A or B"
    end
  end
end
class SomeClass
  include SomeClassMeth
  extend SomeClassMeth
end

# it works as an instance method
bash = SomeClass.new
puts bash.some_method("EDITOR","vim")

# but not as a class method... yet
puts SomeClass.some_method("EDITOR","vim")

但是要小心，如果你使用属性：

module SomeClassMeth
  def some_method(variable, value)
      @a
  end
end
class SomeClass
  @a = "@a in class"
  include SomeClassMeth
  extend SomeClassMeth

  def initialize
    @a = "@a in initialize"
  end

end

# it works as an instance method
bash = SomeClass.new
puts bash.some_method("EDITOR","vim")         #@a in initialize

# but not as a class method... yet
puts SomeClass.some_method("EDITOR","vim")  #@a in class

如何定义一次方法，但同时将它作为类方法和实例方法

1 个答案: