PyMyth: Global variables are evil... WRONG!

[Tim Daneliuk]

On 11/11/2013 08:06 PM, Rick Johnson wrote:
> Globals are justified when they are used to communicate
> information between scopes that otherwise were meant to be
> mutually exclusive.


I think this is certainly the use case most people would suggest.

But I think you may have missed the real reason most modern
designers object to inter-module globals:  The presence of
such entities almost always means the code has been designed
badly.  Whether we're writing pristine OO code (cough, cough)
or more traditional procedural stuff, information hiding
is a good thing.  When and where there is a need for modules
(or programs, or machines, or "clouds", or interstellar space ...)
to share information, my view is this is better done via some sort
of interface/message passing mechanism.  The more "things" that have
to be shared across modules/programs/machines/clouds/space ... the more
*brittle* the end system becomes.

This problem is broader than just variables, BTW.  It exists anytime you
share *anything* across many computational components, especially in highly
parallel and/or distributed systems.  For example, RPCs tend to be lousy
at building high scale distributed system because they usually have
a call-and-wait semantic which will fail if the caller never responds.
In this case the system is sharing the semantics of *time*.  As a general
matter, exactly-once asynchronous messaging tends to be a better implementation
model here.

Just my 2 cents worth.  Interesting read.  Thanks for taking the time
-- 
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Tim Daneliuk     tundra at tundraware.com
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