ruby - 让 ruby​​ 对象响应任意消息？

Question

在 ruby​​ 中是否有 python __getattr__ 的等价物(至少用于查找方法)？

class X(object):
    def __getattr__(self, name):
        return lambda x: print("Calling " + name + ": " + x)

x = X()
x.some_method("some args")

所以它可能是这样的:

class X
    # .. ??? ..
    def default_action(method_name, x)
        puts "Calling {method_name}: {x}"
    end
end

x = X.new()
x.some_method("some args")

Answer 1

是的。如果对象不响应消息，Ruby 将发送一个带有消息选择器和参数的 method_missing 消息给接收者:

class X
  def method_missing(selector, *args, &blk)
    puts "The message was #{selector.inspect}."
    puts "The arguments were #{args.map(&:inspect).join(', ')}."
    puts "And there was #{blk ? 'a' : 'no'} block."
    super
  end
end

x = X.new
x.some_method('some args', :some_other_args, 42)
# The message was :some_method.
# The arguments were "some args", :some_other_args, 42.
# And there was no block.
# NoMethodError: undefined method `some_method'

x.some_other_method do end
# The message was :some_other_method.
# The arguments were .
# And there was a block.
# NoMethodError: undefined method `some_other_method'

请注意，如果您定义了 method_missing，您还应该相应地定义 respond_to_missing?。否则你会得到这样的奇怪行为:

x.respond_to?(:foo) # => false
x.foo               # Works. Huh?

在这种特殊情况下，我们处理所有 消息，因此我们可以简单地定义如下:

class X; def respond_to_missing?(*) true end end

x.respond_to?(:foo) # => true