为什么以下代码在下面给出错误?
require 'open3'
module Hosts
def read
include Open3
popen3("cat /etc/hosts") do |i,o,e,w|
puts o.read
end
end
end
Hosts.read
#=> undefined method `popen3' for Hosts:Class (NoMethodError)
如果我使用完整路径IE Open3::popen3
调用popen3
,则可以使用。但是我已经include
-ED,所以以为我不需要Open3::
位?
谢谢
您已经定义了一种实例方法,但试图将其用作singleton方法。要使您想要的东西,您还必须使用extend
Open3
,而不是include
:
module Hosts
extend Open3
def read
popen3("cat /etc/hosts") do |i,o,e,w|
puts o.read
end
end
module_function :read # makes it available for Hosts
end
现在:
Hosts.read
##
# Host Database
#
# localhost is used to configure the loopback interface
# when the system is booting. Do not change this entry.
##
127.0.0.1 localhost
255.255.255.255 broadcasthost
::1 localhost
=> nil
阅读Ruby中的以下概念将使您更加清晰:
上下文
self
include
vsextend
而不是module_fuction
,您也可以使用以下任何一个实现相同的结果:
module Hosts
extend Open3
extend self
def read
popen3("cat /etc/hosts") do |i,o,e,w|
puts o.read
end
end
end
和
module Hosts
extend Open3
def self.read
popen3("cat /etc/hosts") do |i,o,e,w|
puts o.read
end
end
end