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comp.lang.ruby

undefined local variable

Johan Eriksson

4/25/2008 3:17:00 PM

Hi!

I have some troubles with this.

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

If I type it in irb it works, but when loaded from a function I get this:

undefined local variable or method `att' for main:Object

It refers to the line inside the if-statement. Any ideas?

/Johan
13 Answers

Chris Hulan

4/25/2008 4:47:00 PM

0

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?

Johan Eriksson

4/25/2008 5:32:00 PM

0

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

/Johan

David A. Black

4/25/2008 6:25:00 PM

0

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

--
Rails training from David A. Black and Ruby Power and Light:
INTRO TO RAILS June 9-12 Berlin
ADVANCING WITH RAILS June 16-19 Berlin
INTRO TO RAILS June 24-27 London (Skills Matter)
See http://www.r... for details and updates!

Johan Eriksson

4/25/2008 6:45:00 PM

0

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.

/Johan

David A. Black

4/25/2008 9:20:00 PM

0

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

--
Rails training from David A. Black and Ruby Power and Light:
INTRO TO RAILS June 9-12 Berlin
ADVANCING WITH RAILS June 16-19 Berlin
INTRO TO RAILS June 24-27 London (Skills Matter)
See http://www.r... for details and updates!

Johan Eriksson

4/25/2008 9:39:00 PM

0

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!

/Johan

Johan Eriksson

4/26/2008 4:51:00 PM

0

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!
>
> /Johan
>
>
>

No ideas, anybody? I really don't see why it does not find the variable
there, as it finds it in if-statement.

/Johan

David A. Black

4/26/2008 5:02:00 PM

0

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

--
Rails training from David A. Black and Ruby Power and Light:
INTRO TO RAILS June 9-12 Berlin
ADVANCING WITH RAILS June 16-19 Berlin
INTRO TO RAILS June 24-27 London (Skills Matter)
See http://www.r... for details and updates!

Johan Eriksson

4/26/2008 5:57:00 PM

0

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

--

Johan Eriksson

4/27/2008 4:48:00 PM

0

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

Okay. The problem with this is that name gets bound to "name" => "Alice"
and age to "age" => 20 or something similar. Also I don't know in
advance what attributes the objects will have, as the class is also
generated from a textfile (earlier).

Again, thank for the help!

/Johan


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