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Re: Circular dependencies between libraries - what to do?

From: Thorsten Jolitz
Subject: Re: Circular dependencies between libraries - what to do?
Date: Sun, 21 Sep 2014 12:37:51 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux)

Drew Adams <address@hidden> writes:

>> I have libraries that depend on each other, and I'm not sure
>>  (1) how to use require without introducing circular dependencies?
>>  (2) how to declare their dependencies as MELPA packages?
>> 1. When I put in
>> ,----
>> | A
>> | (require 'B)
>> `----
>> and in
>> ,----
>> | B
>> | (require 'A)
>> `----
>> I'm probably asking for trouble, but B actually does not work
>> without A, and A calls B functions, so they do require each other.
> If these are your own libraries, so that you can modify their code,
> then break them into pieces, and then reorder and recombine pieces.
> Here is the guiding principle:
>   It is not *all* of A that requires *all* of B, and
>   it is not *all* of B that requires *all* of A.
> So look at the code carefully and find which pieces have hard
> (i.e., logical) dependencies on which other pieces.  Keep pieces
> that must be together together; separate (at least logically and
> temporarily) things that can be separated.
> When you have something that makes sense, and thus works, then
> you can try combining pieces to end up with fewer and larger
> ones.  You might find that you end up with more than two files.
> Or you might find that you end up with only one file, but
> better structured (e.g. reordered).
> You will have, at least during the exercise, made any real
> dependencies explicit.  You will understand your code better,
> and you will make it easier to modify it in the future.
> Yes, this can take some time.  Two aids are:
> 1. The byte-compiler, as others have mentioned.
> 2. Commenting-out sections of code temporarily, using, e.g.,
>    `comment-region' (with `C-u' it uncomments).

I ckecked my libraries and figured out that I actually mixed up two
kinds of dependencies (ignore the names, I just made them up):

 - 'technical dependency' -> lib A calls lib B's functions

 - 'functional dependency' -> lib A won't work on a buffer if lib B
   hasn't been activated

in other words, outshine.el requires outorg.el because it calls its
functions, but outorg.el only needs outline-minor-mode with outshine
extensions loaded to work, it does not technically require outshine

So I could actually distribute the (require ...) calls in a sane way
over the libs and solve the issue. 

Thanks for the tips anyway, I will keep them in mind.


I wonder why my announcement of Outshine 2.0 did not make it to this
list - thats like an 8h delay or so.


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