General talk about software patterns

[Ralph Johnson <johnson AT cs.uiuc.edu>]

On Wed, Jan 26, 2011 at 8:25 AM, Douglas C. Schmidt <schmidt AT dre.vanderbilt.edu> wrote:

Hi folks,

  It strikes me that there's a fundamental disconnect at the heart of
this discussion.  Pattern form is best used to give (among other things)
a dispassionate evaluation of the (often contextually related) pros/cons
of recurring design abstractions.  It's not well suited for advocating
the superiority of one particular design abstraction over all others in
all situations.  Al's goal seems to be to convince everyone that MDP
should be *the* solution to all software design problems, which is
clearly (at least to me) not defensible for all the reasons that have
been mentioned here the past months. 

Yes, pattern form is best used to talk about tradeoffs and the pros and cons of various approaches.  One of the biggest problems with the MDP writeup is that it is so one-sided.  It never discusses the costs of MDP.  When I read it, I feel like I'm listening to a used car salesman.  Most engineers get turned off by this approach. I certainly do.

Like most patterns, MDP is an exception, not the norm.    You don't use the Strategy pattern to implement every algorithm.  You use it (sometimes) when you want to make it easier to switch between algorithms.  So, I don't want to be told why MDP is so wonderful.  I want to know when I should consider using it.  And when I should definitely not consider using it.

-Ralph