Question

我正在尝试创建一个新类，它将从ActiveRecord::Base继承，该类需要从字符串中动态生成

"general_systems".camelize.singularize = Class.new < ActiveRecord::Base

但是我一直收到错误：

undefined method `singularize=' for "GeneralSystems":String

我也试过constantize字符串

>> foo = "general_systems".camelize.singularize
=> "GeneralSystem"
>> foo.constantize
NameError: uninitialized constant GeneralSystem
    from /var/lib/gems/1.9.1/gems/activesupport-3.0.5/lib/active_support/inflector/methods.rb:124:in `block in constantize'
    from /var/lib/gems/1.9.1/gems/activesupport-3.0.5/lib/active_support/inflector/methods.rb:123:in `each'
    from /var/lib/gems/1.9.1/gems/activesupport-3.0.5/lib/active_support/inflector/methods.rb:123:in `constantize'
    from /var/lib/gems/1.9.1/gems/activesupport-3.0.5/lib/active_support/core_ext/string/inflections.rb:43:in `constantize'
    from (irb):4
    from /usr/bin/irb:12:in `<main>'
>> foo.constantize = Class.new
NoMethodError: undefined method `constantize=' for "GeneralSystem":String
    from (irb):5
    from /usr/bin/irb:12:in `<main>'

非常感谢任何帮助。

Answer 1

如果您正在使用Rails，它会提供一个名为#constantize的方法，该方法将起作用：

irb(main):017:0> Object.const_get 'House::Owns'
NameError: wrong constant name House::Owns

'House::Owns'.constantize
=> House::Owns

Answer 2

这样的东西？

>> Object.const_set("general_systems".classify, Class.new)
=> GeneralSystem
>> GeneralSystem.new
=> #<GeneralSystem:0x105b0f738>

Answer 3

klazz = Class.new(ActiveRecord::Base) do
  def do_something_fun(param1)
    param1.have_fun!
  end
end

klazz_name = "general_systems".singularize.classify
Object.const_set(klazz_name, klazz)

Answer 4

从Ruby Book安装程序中包含的“The Book of Ruby”中查看此示例。

puts("What shall we call this class?> ")
className = gets.strip().capitalize()
Object.const_set(className,Class.new)
puts("I'll give it a method called > 'myname'" ) 
className = Object.const_get(className)
className::module_eval{
  define_method(:myname){ 
    puts("The name of my class is '#{self.class}'" ) 
 } }
 x = className.new x.myname

Answer 5

如果您的字符串包含命名空间，您可以使用：

require 'rubygems'
require 'active_support/inflector'
parent=String # using String to get a self contained example
# require 'active_record'   # uncomment for ActiveRecord::Base as parent class
# parent=ActiveRecord::Base # uncomment for ActiveRecord::Base as parent class
namespace = 'A::B::general_systems'.split('::') 
class_name = namespace.pop 
namespace = namespace.inject(Object) do |mod, name|
  if mod.constants.collect{|sym| sym.to_s}.include? name.classify
    mod.const_get name.classify
  else
    mod.const_set name.classify, Module.new
  end
end

klass = if namespace.constants.include? class_name.classify
  namespace.const_get class_name.classify
else
  namespace.const_set class_name.classify, Class.new(parent)
end

object = klass.allocate # allocate new object of klass
object.send :initialize # initialize object
object.class
object.class.superclass

Answer 6

给出：

class Banana
end

您可以使用以下方式在纯Ruby中获取该类：

Object.const_get 'Banana'
=> Banana

或者如果您使用的是Rails：

'Banana'.constantize
=> Banana

Answer 7

试

>> "general_systems".classify
=> "GeneralSystem"

Ruby字符串到类名

7 个答案: