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July 23, 2013



Hey Michael,

Thanks, this clarifies the following answer you posted in [1]:

"It’s a funny thing about the design principles. I think that often if you take one, you get many of the others by implication. If you concentrate on SRP, you can end up with OCP without even thinking about it. I think the same is true of OCP.. If you really push it, you will end up with modules with single responsibilities..."

[1] http://web.archive.org/web/20091225221756/http://blog.objectmentor.com/articles/2009/02/26/10-papers-every-programmer-should-read-at-least-twice



Ooer, careful, Michael, you're using that word, "Closure," that already has perfectly good credentials elsewhere. Your, "Closure," is neither the mathematical, "Closure," nor anything related to the lambda, "Closure." Just because it's, "Closed for modification," doesn't mean it's an example of a, "Closure." It's an example of, "Being closed."

Vic Ripa

Hi Michael,
the idea that the SOLID principles are all connected to a common notion (responding to change) has been explored here by Giorgio Sironi:


That, in turn, is inspired by Carlo Pescio's work on the physics of software.


I think that is an oversimplification. I'm not sure, whether I'd even agree on the statement that SRP implies OCP.

You could construct a perfectly valid component with exactly one responsibility. Let's call it a dispatcher. If that dispatcher is implemented as cascading if-then-else-statements, then you are required to change that implementation in order to introduce new features.

Via a wrapper you could argue that there is no need for a change in the dispatcher-component. But in that case you'd spread the responsibility for a dispatch on the wrapper and the dispatcher.

But I agree that small and focussed abstractions tend to improve encapsulation.

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This is a topic that's near to my heart... Many thanks! Where are your contact details though?


I hardly drop remarks, however i did a feew searchkng annd wound up here Michael Feathers: The Single Responsibility annd Open/Closed Principle are the Same. And I actually doo have a couple of questions for you if it's allright. Could it be only me or does it look as if like a few of the remarks look as if they are left by brain dead folks? :-P And, if you are posting on additional places, I'd like to keep up with everything freh you have to post. Could you make a list of all of your public pages like your Faacebook page, twitter feed, or linkedin profile?


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