ruby – 如何在类变量中定义的lambda / Proc中使用实例变量？

发布时间：2020-12-17 02:42:55 所属栏目：百科来源：网络整理

导读：我写了以下代码： class Actions def initialize @people = [] @commands = { "ADD" = -(name){@people name },"REMOVE" = -(n=0){ puts "Goodbye" },"OTHER" = -(n=0){puts "Do Nothing" } } end def run_command(cmd,*param) @commands[cmd].call param if

我写了以下代码：

class Actions
  def initialize
    @people = []
    @commands = {
      "ADD" => ->(name){@people << name },"REMOVE" => ->(n=0){ puts "Goodbye" },"OTHER" => ->(n=0){puts "Do Nothing" }
    }
  end
  def run_command(cmd,*param)
    @commands[cmd].call param if @commands.key?(cmd)
  end
  def people
    @people
  end
end
act = Actions.new

act.run_command('ADD','joe')
act.run_command('ADD','jack')
puts act.people

但是,当@commands哈希是类变量时,哈希内部的代码不知道@people数组.

如何使@commands哈希成为类变量并仍然能够访问特定的对象实例变量？

解决方法

您可以在调用lambda时使用 instance_exec为lambda提供适当的上下文,查找注释以查看更改：

class Actions
  # Move the lambdas to a class variable,a COMMANDS constant
  # would work just as well and might be more appropriate.
  @@commands = {
    "ADD"    => ->(name)  { @people << name   },"REMOVE" => ->(n = 0) { puts "Goodbye"    },"OTHER"  => ->(n = 0) { puts "Do Nothing" }
  }
  def initialize
    @people = [ ]
  end
  def run_command(cmd,*param)
    # Use instance_exec and blockify the lambdas with '&'
    # to call them in the context of 'self'. Change the
    # @@commands to COMMANDS if you prefer to use a constant
    # for this stuff.
    instance_exec(param,&@@commands[cmd]) if @@commands.key?(cmd)
  end
  def people
    @people
  end
end

（编辑：李大同）

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