如何使用类变量中定义的lambda/Proc中的实例变量

Question

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

然而，当@commands散列是类变量时，散列中的代码不知道@people数组，这是可行的。

如何使@commands散列成为类变量，并且仍然能够访问特定的对象实例变量？

Answer 1

当您调用Lambda时，可以使用instance_exec为它们提供适当的上下文，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

Answer 2

编辑遵循@VictorMoroz和@mu的建议：

class Actions
  def initialize
    @people = []
  end
  def cmd_add(name)
    @people << name
  end
  def cmd_remove
    puts "Goodbye"
  end
  def cmd_other
    puts "Do Nothing"
  end
  def people
    p @people
  end
  def run_command(cmd, *param)
    cmd = 'cmd_' + cmd.to_s.downcase
    send(cmd, *param) if respond_to?(cmd)
  end
end
act = Actions.new
act.run_command('add', 'joe')
act.run_command(:ADD, 'jill')
act.run_command('ADD', 'jack')
act.run_command('people') # does nothing
act.people

或

class Actions
  ALLOWED_METHODS = %w( add remove other )
  def initialize
    @people = []
  end
  def add(name)
    @people << name
  end
  def remove
    puts "Goodbye"
  end
  def other
    puts "Do Nothing"
  end
  def people
    p @people
  end
  def run_command(cmd, *param)
    cmd = cmd.to_s.downcase
    send(cmd, *param) if ALLOWED_METHODS.include?(cmd)
  end
end
act = Actions.new
act.run_command('add', 'joe')
act.run_command(:add, 'jill')
act.run_command('add', 'jack')
act.run_command('people') # does nothing
act.people