Question

给定一个类实例和一个字符串，如何将字符串转换为引用实例？

class Room
  def enter
    puts "Welcome!"
  end
end

# Rooms are predefined
lounge = Room.new
kitchen = Room.new
study = Room.new

puts "Which room would you like to go to?"
print "> "
room = gets.strip

# User types "lounge"

room.enter # => undefined method `enter' for "lounge":String (NoMethodError)

我理解为什么我得到NoMethodError，但我无法弄清楚如何转换room字符串以引用名为lounge的Room的现有实例。

Answer 1

或许试图按照房间来映射房间？

class Room

  def enter
    puts "Welcome!"
  end
end

# Rooms are predefined
rooms = %w[lounge kitchen study].inject({}) { |f,c| f.update c => Room.new }

puts "Which room would you like to go to?"
print "> "
if room = rooms[gets.strip]
  room.enter
end

甚至更简单：

class Room

  def initialize room_type
    @room_type = room_type
  end

  def enter
    return puts 'Unsupported room type' unless %w[
      lounge kitchen study
    ].include?(@room_type)
    puts "Welcome to #{@room_type}!"
  end

end

puts "Which room would you like to go to?"
print "> "
room = Room.new(gets.strip)
room.enter

Answer 2

room_name = gets.strip.capitalize
room = Kernel.const_get(room_name)
room.enter

如果您require "active_support/all"（部分Rails）可以执行此操作：

room = gets.strip.camelize.constantize
room.new.enter

修改

正如田人指出的那样，require "active_support/core_ext/string/inflections"会更有效率。

Answer 3

class Room
  attr_reader :name

  def initialize(name)
    @name = name
  end

  def enter
    puts "Welcome to #{@name}!"
  end
end

# Rooms are predefined
rooms = ["lounge", "kitchen", "study"].map(&Room.method(:new))

puts "Which room would you like to go to?"
print "> "
name = gets.strip

# Just an example (not using find to avoid nil.enter)
p rooms.select{ |room| room.name == name }.map(&:enter)

Answer 4

您可以使用eval方法动态执行一段ruby脚本。在这种情况下，eval(room)会为您提供房间实例。

然而，这是非常危险的方法，因为它允许最终用户执行代码。为了防止代码执行，您最好验证它是定义的房间变量之一：

eval(room).enter if local_variables.include?(room.to_sym)

Answer 5

我最终在散列中将每个Room对象存储为初始化时的类变量。这允许您通过哈希引用每个实例：

class Room
  @@rooms = {}

  def initialize(name)
    @@rooms.store name, self
  end

  def rooms
    @@rooms
  end

  def enter
    puts "Welcome!"
  end
end

# Rooms are predefined
lounge = Room.new('lounge')
kitchen = Room.new('kitchen')
study = Room.new('study')

puts "Which room would you like to go to?"
print "> "
new_room = gets.strip

lounge.rooms[new_room].enter if lounge.rooms.has_key? new_room

将字符串转换为现有的类实例

5 个答案: