mailThe singleton design pattern for the old 'self.relax.data' data structure.


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Posted by Edward d'Auvergne on March 07, 2007 - 09:07:
Hi,

After careful thought about design patterns, I've decided to try to
use the singleton pattern for the old 'self.relax.data' data
structure.  See http://en.wikipedia.org/wiki/Singleton_pattern for
more information about this design pattern.  I'll try to use the
second simple example under the heading 'Python Borg pattern'.  The
benefit of this pattern is that each module can use the code:

from data import Data
relax_data = Data()

As Data will be a singleton if two modules used by relax instantiate
the Data class then the global 'relax_data' in both modules will be
the same instance.  Therefore if a method from the
'special_fns.model_free' module modifies the data structure, all the
other relax modules using the singleton will see the changes.  The
benefit of this pattern is that the data structure is similar in
concept to a global variable but only modules utilising it will have
it in one of their namespaces.  Also 'self.relax.data' will not need
to be passed around inside the program, simplifying the code.  What do
you think of the idea?

Cheers,

Edward


P.S. Another idea would be to create the variable 'relax_data.current_run'. The 'relax_data' singleton structure will be a dictionary type as proposed in the redesign discussions, hence you would have say 'relax_data['m5']' being another object containing all the model-free model m5 data, but the variable could be part of the singleton data structure. The data object of the current run could then be accessed as 'data = relax_data[relax_data.current_run]'. This is probably an anti-pattern so please feel free to suggest better ideas.



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