On May 13, 2015, at 11:07 PM, Brian Craft <craft.br...@gmail.com> wrote:
> http://en.wikipedia.org/wiki/Encapsulation_(object-oriented_programming)#As_information_hiding_mechanism
>  
> <http://en.wikipedia.org/wiki/Encapsulation_(object-oriented_programming)#As_information_hiding_mechanism>

In an environment where you can’t trust your co-workers(!), you certainly want 
to hide *mutable* data so they can’t modify your objects’ state. When you 
remove mutability, there’s a lot less damage they can do and they it’s really 
more about which pieces of the system do you not want them to "use" (in terms 
of functional APIs).

The "Clojure Way" seems to be "just make all functions public — they might be 
useful to someone" although that then restricts what refactoring you can do in 
future compared to exposing a smaller surface area. Since you can always call 
private functions anyway (and access private data directly), you really need 
conventions — and code review — to prevent abuse, and at that point having 
foo.api and foo.impl namespaces — and a convention to not use foo.impl outside 
of foo.api — is very reasonable and even automatically enforceable through 
tooling.

When I first started doing Clojure (five years ago — yikes! feels like 
yesterday!) I still had an OOP mindset around data hiding and I used defn- and 
^:private a lot (well, ^{:private true} back then I guess). These days I tend 
to make all my functions public and use namespaces if necessary to clearly 
delineate APIs vs implementations. A def of immutable data tends to be public 
too. It’s rare that I feel the need to make things private since immutability 
means no one can "abuse" my data or my functions.

Sean Corfield -- (904) 302-SEAN
An Architect's View -- http://corfield.org/

"Perfection is the enemy of the good."
-- Gustave Flaubert, French realist novelist (1821-1880)



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