# Creating classes only when needed?

**URL:** <https://www.ruby-forum.com/t/creating-classes-only-when-needed/101804>\
**Category:** Ruby\
**Created:** [February 7, 2006, 12:32am UTC](https://www.ruby-forum.com/t/creating-classes-only-when-needed/101804 "2006-02-07T00:32:31Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![PaatschS\_Bernd](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/fbc32d/32.png) [@PaatschS\_Bernd](https://www.ruby-forum.com/u/PaatschS_Bernd)\
**Post date:** [February 7, 2006, 12:32am UTC](https://www.ruby-forum.com/t/creating-classes-only-when-needed/101804/1 "2006-02-07T00:32:31Z")

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Hello,

I am fairly new to ruby and need some help  
I am structuring my code using classes.  
The application I work on requires input data. This data may require all  
or  
some of the classes I create. Instead of having a section in the main  
code  
creating all classes I would like to create only those classes that I  
need  
while reading the data. However I do not know how to do that. Below is  
the  
outline of my code.

Any suggestions

class ReadFileFactory

# handles calling the right class to for reading the data

# from database, from CSV-file, etc.

… code goes here …  
end

class CSVReadFile( externalClass, nameID )

# handles reading data using a csv-file and assigning it to the

appropriate  
Hash  
… code goes here …  
case signal  
when nameID  
externalClass.getLine(tempStore)  
when …  
end

class AddSubscriber

# handles adding a subscriber

… code goes here …  
end

# main program

# Initialize I don’t like that

class1 = Class1.new;  
class2 = Class2.new; #etc  
test = ReadFileFactory.start\_csv\_readfile(“sample.csv”)

test.processingFile( class1 )

# I rather would have something like that

ReadFileFactory.start\_csv\_readfile(“sample.csv”) will return only the  
classes I need.

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<div class="post-metadata">

**Author:** ![PaatschS\_Bernd](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/fbc32d/32.png) [@PaatschS\_Bernd](https://www.ruby-forum.com/u/PaatschS_Bernd)\
**Post date:** [February 7, 2006, 12:44am UTC](https://www.ruby-forum.com/t/creating-classes-only-when-needed/101804/2 "2006-02-07T00:44:42Z")

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DÅ?a Utorok 07 Február 2006 00:30 Paatsch, Bernd napísal:

> Any suggestions  
> … code goes here …
> 
> # I rather would have something like that
> 
> ReadFileFactory.start\_csv\_readfile(“sample.csv”) will return only the  
> classes I need.

Well, your example is fairly generic, so I’ll be guessing what you  
really want  
to do.

I think you started on the right track with the factory. If I understand  
you  
right, that one provides an adapter for the way the data is stored. You  
could  
continue by storing the data type in the adapter, or whatever it  
returns, and  
then processing it into some sort of facade processing class that will  
internally decide what processing is required for what data and hide  
this  
from the “main” script body.

David V.  
Might be horribly, horribly wrong

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<div class="post-metadata">

**Author:** ![PaatschS\_Bernd](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/fbc32d/32.png) [@PaatschS\_Bernd](https://www.ruby-forum.com/u/PaatschS_Bernd)\
**Post date:** [February 7, 2006, 1:36am UTC](https://www.ruby-forum.com/t/creating-classes-only-when-needed/101804/3 "2006-02-07T01:36:34Z")

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On 2/6/06, Paatsch, Bernd [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> Hello,
> 
> I am fairly new to ruby and need some help  
> I am structuring my code using classes.  
> The application I work on requires input data. This data may require all or  
> some of the classes I create. Instead of having a section in the main code  
> creating all classes I would like to create only those classes that I need  
> while reading the data. However I do not know how to do that.

Class names are constants. To get a reference to a class from a name  
(String or Symbol):

klass = Object.const\_get(classname)

Here’s an example to get you going:

class Class1  
def run  
puts “You chose class 1”  
end  
end

class Class2  
def run  
puts “You chose class 2”  
end  
end

# this roundabout way of defining the class name is to emphasise

# that you can construct the class name dynamically

n = “1”  
classname = “Class#{n}”

klass = Object.const\_get(classname)  
obj = klass.new  
obj.run  
#=\> You chose class 1"

Regards,

Sean