From: Johan Eriksson <johan@...>
Date: 2008-04-27T02:57:28+09:00
Subject: Re: undefined local variable

Hi --

David A. Black wrote:
> Hi --
> 
> On Sat, 26 Apr 2008, Johan Eriksson wrote:
> 
>> Hi --
>>
>> David A. Black wrote:
>>> Hi --
>>>
>>> On Sat, 26 Apr 2008, Johan Eriksson wrote:
>>>
>>>> Hi --
>>>>
>>>> David A. Black wrote:
>>>>> Hi --
>>>>>
>>>>> On Sat, 26 Apr 2008, Johan Eriksson wrote:
>>>>>
>>>>>> Chris Hulan wrote:
>>>>>>> On Apr 25, 11:16 am, Johan Eriksson <jo...@johaneriksson.se> wrote:
>>>>>>>> Hi!
>>>>>>>>
>>>>>>>> I have some troubles with this.
>>>>>>>>
>>>>>>>>            obj_as_list.each do |att|
>>>>>>>>              if att[1].is_a?(String)
>>>>>>>>                att[1] = "'#{att[1]'"
>>>>>>> You're missing a '}' here ----------^
>>>>>>>
>>>>>>> does that help?
>>>>>>>
>>>>>>
>>>>>> Nope. I am providing the surrounding function here. (It is defined 
>>>>>> inside a class.)
>>>>>>
>>>>>>    def load_from_file(filename)
>>>>>>      require 'yaml'
>>>>>>      yaml_dict = YAML::load(File.open(filename))
>>>>>>      object_list = []        #The list that should be returned
>>>>>>      yaml_dict[yaml_dict.keys[0]].each do |yaml_obj|
>>>>>>        new_obj = self.class.new
>>>>>>        yaml_obj.each do |obj|
>>>>>>          obj_as_list = obj.to_a
>>>>>>          obj_as_list.each do |att|
>>>>>>            if att[1].is_a?(String)
>>>>>>              att[1] = "'#{att[1]}'"
>>>>>>            end
>>>>>>            str = "new_obj.#{att[0]} = #{att[1]}"
>>>>>>            eval(str)
>>>>>>          end
>>>>>>        end
>>>>>>        object_list << new_obj
>>>>>>      end
>>>>>>      object_list
>>>>>>    end
>>>>>>
>>>>>> And the error:
>>>>>>
>>>>>>     NameError: undefined local variable or method `att' for 
>>>>>> main:Object
>>>>>
>>>>> If att[1] is, say, :att, then "#{att[1]}" is "att" and you've got a
>>>>> dangling att. The whole eval thing seems extremely fragile (which eval
>>>>> things usually are). I imagine there's a more robust and probably
>>>>> shorter way to do this, but I'm not sure what the data coming in and
>>>>> out are supposed to be like.
>>>>>
>>>>>
>>>>> David
>>>>>
>>>>
>>>> I am almost positive that there is, given that I'm pretty much a 
>>>> noob at ruby. The whole thing is a class_eval too. The idea is to 
>>>> add this function to a class that has just been created based on a 
>>>> textfile. The function will receive a file that includes a yaml 
>>>> description of instances of the class, and the function then makes 
>>>> these instances and sends them back as a list. I think some 
>>>> fragility is okay, though I'd be keen on learning better ways to do 
>>>> this. Around the entire function is
>>>>
>>>> the_class.class_eval %{
>>>>     the function...
>>>> }
>>>>
>>>> I am confused about why it doesn't work though.
>>>
>>> Can you give some sample YAML input? I'm still not quite picturing it.
>>>
>>>
>>> David
>>
>> This is a simple example:
>>
>> dogs:
>>    - name        : Fido
>>      age         : 2
>>
>>    - name        : Rufus
>>
>>    - name        : Doggie
>>      age         : 4
>>
>>    - name        : Puppy
>>      age         : 1
>>
>> The function should then create four instances of dog, assign them the 
>> names and ages specified, put them in a list and return them.
>>
>> Thanks for taking the time to help me out!
> 
> Why not do this (or something similar):
> 
> require 'yaml'
> 
> class Dog
>   attr_accessor :name, :age
> end
> 
> animals = YAML.load(<<EOA)
> dogs:
>     - name        : Fido
>       age         : 2
> 
>     - name        : Rufus
> 
>     - name        : Doggie
>       age         : 4
> 
>     - name        : Puppy
>       age         : 1
> EOA
> 
> dogs = animals["dogs"]
> dog_objects = dogs.map do |name,age|
>   d = Dog.new
>   d.name = name
>   d.age = age
>   d
> end
> 
> p dog_objects
> 
> 
> David
> 

Thanks a lot! I think this will be very helpful. I didn't know map 
worked like this. I'll need to adapt it to work even though I don't know 
the name of the class in advance, but that's workable, right?

/Johan

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