即时确定方法的可见性 [英] Determining method's visibility on the fly

问题描述

我正在编写一个将在类中定义实例方法的方法；类似于 attr_accessor 的东西:

I am writing a method that will define an instance method inside a class; something similar to attr_accessor:

class Foo
  custom_method(:foo)
end

我已经通过向 Module 模块添加 custom_method 函数并使用define_method 定义方法来实现这一点，该方法工作正常.但我无法弄清楚如何考虑类的可见性属性.例如，在下面的类中

I have implemented that by adding custom_method function to the Module module, and defining the method with define_method, which works fine. But I cannot figure out how to take into account visibility attributes from the class. For example, in the following class

class Foo
  custom_method(:foo)
private
  custom_method(:bar)
end

第一个生成的方法 (foo) 必须是公共的，第二个 (bar) 必须是私有的.我怎么做?或者，我如何找到调用我的 custom_method 的上下文:private、public 或 protected?

the first generated method (foo) must be public, and the second one (bar) must be private. How do I do that? Or, how do I find the context in which my custom_method is called: private, public, or protected?

谢谢！

推荐答案

在尝试了一段时间后，我完全感到困惑.最初，我认为 Ruby 在调用 Module#define_method 时考虑了默认可见性(公共、私有或受保护).但事实证明，在 Ruby 版本 <= 2.0 上，情况并非如此:

After experimenting with this for a bit, I'm completely baffled. Initially, I thought that Ruby took the default visibility (public, private, or protected) into account when you call Module#define_method. It turns out though that on Ruby versions <= 2.0, that's not the case:

class Foo
  private
  define_method :foo do
    puts "Foo called!"
  end
end

Foo.new.foo # Prints "Foo called!"

在 Ruby 2.1+ 上，它更令人困惑.Module#define_method 似乎考虑了默认方法的可见性:

On Ruby 2.1+, it's even more confusing. Module#define_method seems to take default method visibility into account:

class Foo
  private
  define_method :foo do
    puts "Foo called!"
  end
end

Foo.new.foo # NoMethodError: private method `foo' called for #<Foo:0x8cb75ac>

但它仅在您直接从类内部调用 define_method 时才有效.调用一个方法，然后调用 define_method 不起作用:

But it only works when you are calling define_method from directly inside the class. Calling a method which then calls define_method doesn't work:

class Foo
  def self.hello_on name
    define_method name do
      puts "Hello, #{name}!"
    end
  end

  private
  hello_on :foo
end

Foo.new.foo # Prints "Hello, foo!"

该死的红宝石！为什么?

好的，这需要采取绝望的措施......

Okay, this calls for desperate measures...

module DefaultMethodVisibilityAccessor
  attr_reader :current_default_method_visibility

  def public(*args)
    @current_default_method_visibility = :public if args.empty?
    super
  end
  def protected(*args)
    @current_default_method_visibility = :protected if args.empty?
    super
  end
  def private(*args)
    @current_default_method_visibility = :private if args.empty?
    super
  end
end

class Module
  prepend DefaultMethodVisibilityAccessor
end

module MethodDefiner
  def hello_on name
    define_method name do
      puts "Hello, #{name}!"
    end

    case current_default_method_visibility
    when :public
      public name
    when :protected
      protected name
    when :private
      private name
    end
  end
end

用法:

class Foo
  extend MethodDefiner
  hello_on :foo
  private
  hello_on :bar
end

Foo.new.foo # Prints "Hello, foo!"
Foo.new.bar # NoMethodError: private method `bar' called for #<Foo:0x8ec18fc>

那里，固定！

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