# Choosing a module name at runtime

**URL:** <https://www.ruby-forum.com/t/choosing-a-module-name-at-runtime/175404>\
**Category:** Ruby\
**Created:** [September 13, 2009, 12:25am UTC](https://www.ruby-forum.com/t/choosing-a-module-name-at-runtime/175404 "2009-09-13T00:25:59Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![captaffy](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/f04885/32.png) [@captaffy](https://www.ruby-forum.com/u/captaffy)\
**Post date:** [September 13, 2009, 12:25am UTC](https://www.ruby-forum.com/t/choosing-a-module-name-at-runtime/175404/1 "2009-09-13T00:25:59Z")

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My application chooses at runtime the input format of some data, for  
example :xml or :mysql. Then, the app instantiates a DataManager. The  
DataManager class should ‘include’ the appropriate Module (either  
DataIOXML or DataIOMySQL).  
I tried to use include in the initialize method of DataManager, but that  
doesn’t work.  
Can I include a module in the initialize method of the class? If yes,  
how?  
If no: Any other ways how I can choose the correct module to include at  
runtime?

Important: All the information about Modules and file names is stored in  
the DataManager class. My app only knows the DataManger class itself,  
not the names of the modules (so I can’t subclass separate IO classes  
from DataManager, and instantiate them directly from my app).

Here’s the example code for the app, the DataManger class, and the :xml  
Module:

#! /usr/bin/ruby -w

# main app

# 

# here, only the name ‘DataManager’ and the IO format (:xml or :mysql)

is known,

# not the name of the format-specific module.

require “DataManager.rb”  
dm = DataManager.new(:xml)  
dm.say\_something

# DataManager.rb

class DataManager

# theDataManager class knows all possible IO formats, and the

# corresponding Module names:

@@io\_mixins = {  
:xml =\> ‘DataIOXML’,  
:mysql =\> ‘DataIOMySQL’,  
}

def initialize(format=:xml)

```
unless @@io_mixins.include? format
  raise NotImplementedError, "IO Format #{format} unknown"
end

require @@io_mixins[format]+".rb"
# the next line causes an error
include DataIOXML

```

end  
end

# DataIOXML.rb

# XML-specific module

module DataIOXML  
def say\_something  
puts “I’m DataIOXML”  
end  
end

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<div class="post-metadata">

**Author:** ![captaffy](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/f04885/32.png) [@captaffy](https://www.ruby-forum.com/u/captaffy)\
**Post date:** [September 13, 2009, 12:41am UTC](https://www.ruby-forum.com/t/choosing-a-module-name-at-runtime/175404/2 "2009-09-13T00:41:42Z")

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On Sep 12, 2009, at 3:26 PM, John Smirnoff wrote:

> at  
> runtime?

You want the “extend” method, not the “include” method:

module A  
def foo  
“A: foo”  
end  
end

module B  
def foo  
“B: foo”  
end  
end

class C  
def initialize which  
extend(which == :a ? A : B)  
end

def metaclass; class \<\< self; self end end  
end

p C.new(:a).metaclass.ancestors  
p C.new(:b).metaclass.ancestors

Hope that helps.

* * *

Aaron P.  
[http://tenderlovemaking.com](http://tenderlovemaking.com)

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<div class="post-metadata">

**Author:** ![captaffy](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/f04885/32.png) [@captaffy](https://www.ruby-forum.com/u/captaffy)\
**Post date:** [September 13, 2009, 1:07am UTC](https://www.ruby-forum.com/t/choosing-a-module-name-at-runtime/175404/3 "2009-09-13T01:07:59Z")

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Aaron P. wrote:

> You want the “extend” method, not the “include” method:

Thanks!