Ruby . vs ：：(点与双冒号)用于调用方法

发布于06月15日

我正在从Poignant Guide to Ruby中学习Ruby，在一些代码示例中，我遇到了双冒号和点的用法，它们似乎用于相同的目的:

File::open( 'idea-' + idea_name + '.txt', 'w' ) do |f|
   f << idea
end

在上面的代码中，双冒号用于访问File类的open方法.然而，我后来遇到了出于同样目的使用点的代码:

require 'wordlist'
# Print each idea out with the words fixed
Dir['idea-*.txt'].each do |file_name|
   idea = File.read( file_name )
   code_words.each do |real, code| 
     idea.gsub!( code, real )
   end
puts idea
end

这一次，一个点被用来访问File类的read方法.以下两者之间的区别是什么:

File.read()

和

File::open()

推荐答案

这是scope resolution operator.

维基百科的一个例子:

module Example
  Version = 1.0

  class << self # We are accessing the module's singleton class
    def hello(who = "world")
       "Hello #{who}"
    end
  end
end #/Example

Example::hello # => "Hello world"
Example.hello "hacker" # => "Hello hacker"

Example::Version # => 1.0
Example.Version # NoMethodError

# This illustrates the difference between the message (.) operator and the scope
# operator in Ruby (::).
# We can use both ::hello and .hello, because hello is a part of Example's scope
# and because Example responds to the message hello.
#
# We can't do the same with ::Version and .Version, because Version is within the
# scope of Example, but Example can't respond to the message Version, since there
# is no method to respond with.