Rails - Feb 2006 - Custom view helpers

Hi all,

I would like to write some custom helpers like the ones available as  
form helpers text_field, text_area and the like. My first try was this:

custom_helper(obj, meth)
   ''some_string'' + obj.send(meth) +
''some_other_string''
end

Object and method are being passed as symbols like this:

custom_helper(:person, :name)

and Ruby rightfully complains that the symbol person does not have a  
method named name. Second try was this. @person is an instance  
variable of the controller, right?

custom_helper(obj, meth)
   ''some_string'' + self.get_instance_variable(obj).send(meth)
+
   ''some_other_string''
end

and I get "`person'' is not allowed as an instance variable
name".

How does Rails do that? I can see the text_field being Implemented  
like this:

InstanceTag.new(object, method, self)

but I have no idea what the InstanceTag class does or where I can  
find it.

Many thanks in advance for any pointers!

--Nicky

2006/2/1, Nickolay Kolev <nmkolev@uni-bonn.de>:
> Hi all,
>
> I would like to write some custom helpers like the ones available as
> form helpers text_field, text_area and the like. My first try was this:
>
> custom_helper(obj, meth)
>    ''some_string'' + obj.send(meth) +
''some_other_string''
> end
>
In your views just call custom_helper(@person, :name)

> In your views just call custom_helper(@person, :name)
That was kind of obvious. I want to know how the ''official''
helpers
are implemented so that they can work with symbols as well as stings  
being passed as parameters.

Nicky

Source code: actionpack/lib/action_view/helpers/form_helper.rb

2006/2/1, Nickolay Kolev <nmkolev@uni-bonn.de>:
> > In your views just call custom_helper(@person, :name)
>
> That was kind of obvious. I want to know how the
''official'' helpers
> are implemented so that they can work with symbols as well as stings
> being passed as parameters.
>
> Nicky

> That was kind of obvious. I want to know how the
''official'' helpers
> are implemented so that they can work with symbols as well as  
> stings being passed as parameters.
I had worked around it when I needed it but stumbled across the  
solution today. This is an excerpt from code for the  
error_messages_for method:

instance_variable_get("@#{obj.to_s}")

I had not realised the parameter to instance_variable_get should be a  
string or a symbol with an @-sign up front. I guess I should have  
looked it up first, it is well documented in the Pickaxe book.

Nicky