Question

我正在从Poignant Guide to Ruby学习Ruby，在一些代码示例中，我遇到了似乎用于相同目的的双冒号和点的使用：

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open类的File方法。但是，后来我遇到了使用点来实现相同目的的代码：

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，正在使用一个点来访问read类的File方法。有什么区别：

File.read()

和

File::open()

Answer 1

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.

。 vs ::（点与双冒号）用于调用方法

1 个答案: