So you want a transition phase where existing consuming code can work with
both data shapes, and then start fixing functions one at a time to use the
new data shape, until you reach the point where you have only the new data
shape produced / consumed in your application?
Current consumer functions expect the data to behave as a vector: calling
seq on it should produce an deterministically ordered list of property
values, calling nth should work, etc.
Upgraded consumer functions will expect the data to behave as a map, so be
able to pick keyword keys.
You could implement a transitional protocol which would behave differently
depending on how data is accessed (then delegating to the underlying
fields).
You would probably have to make some compromises during this transition
phase. E.G. refactored consumer functions would not be able to call (seq)
on the map (or they would get the data vector back).
HTH,
-- Laurent
2014-05-22 10:17 GMT+02:00 Jakub Holy <jakub.h...@iterate.no>:
> I have a nested data structure, used by a bunch of functions that presume
> knowledge of its structure, and I wonder how to change a part of the
> structure in a safe way, preferably in small incremental steps, rather than
> having my code broken until I update all the functions and tests for the
> new structure. I believe many of you must have experiences with this, would
> you care to share some tips?
>
> The data structure is first built incrementally and the collected data is
> later summarized. Instead of replacing the raw data with their summary, I
> want to keep both, so I want to wrap the data with a map; i.e. from:
> { <id> [ data...] } ;; later replaced with {<id> summary}
> to
> {<id> {:data [data...], :summary ...}
>
> I have a number of functions operating on the structure and tests for
> those functions (with test data that also need to be updated w.r.t. the
> refactoring).
>
> When I change one of the functions to produce the new data structure (i.e.
> data wrapped in a map instead of the data itself), everything else breaks.
> So I fix some tests and another function and get even more failures. This
> does not feel as a good way to do it as I prefer to have limited
> red<http://www.infoq.com/presentations/The-Limited-Red-Society>and am fond of
> parallel
> change<http://theholyjava.wordpress.com/wiki/development/parallel-design-parallel-change/>for
> that reason.
>
> Ideally, I would have an automated refactoring or the possibility to wrap
> the data in some kind of a two-faced proxy that could behave both as a
> vector (towards the old code) or as a map containing the vector (towards
> the updated code) [some thing like lenses/cursor?!]. I haven't either so I
> guess the only option remaining is a well-controlled process of updating
> the structure and code. Any advice?
>
> Thank you! /Jakub
> --
> *Forget software. Strive to make an impact, deliver a valuable change.*
>
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>
> Jakub Holy
> Solutions Engineer | +47 966 23 666
> Iterate AS | www.iterate.no
> The Lean Software Development Consultancy
> - http://theholyjava.wordpress.com/ -
>
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