ruby - 如何在 Ruby 中初始化模块的实例变量？

Question

我有一些模块，我想在其中使用实例变量。我目前正在像这样初始化它们:

module MyModule
  def self.method_a(param)
    @var ||= 0
    # other logic goes here
  end
end

我也可以调用一个 init 方法来初始化它们:

def init
  @var = 0
end

但这意味着我必须记住始终调用它。

有更好的方法吗？

Answer 1

在模块定义中初始化它们。

module MyModule
  # self here is MyModule
  @species = "frog"
  @color = "red polka-dotted"
  @log = []

  def self.log(msg)
    # self here is still MyModule, so the instance variables are still available
    @log << msg
  end
  def self.show_log
    puts @log.map { |m| "A #@color #@species says #{m.inspect}" }
  end
end

MyModule.log "I like cheese."
MyModule.log "There's no mop!"
MyModule.show_log #=> A red polka-dotted frog says "I like cheese."
                  #   A red polka-dotted frog says "There's no mop!"

这将在定义模块时设置实例变量。请记住，您始终可以稍后重新打开模块以添加更多实例变量和方法定义， 或重新定义现有的:

# continued from above...
module MyModule
  @verb = "shouts"
  def self.show_log
    puts @log.map { |m| "A #@color #@species #@verb #{m.inspect}" }
  end
end
MyModule.log "What's going on?"
MyModule.show_log #=> A red polka-dotted frog shouts "I like cheese."
                  #   A red polka-dotted frog shouts "There's no mop!"
                  #   A red polka-dotted frog shouts "What's going on?"