Re: lua_which

[Hao Wu <wuhao.wise@...>]

On Monday, October 27, 2014, Dirk Laurie <dirk.laurie@gmail.com> wrote:
> 2014-10-27 8:38 GMT+02:00 Hao Wu <wuhao.wise@gmail.com>:
>
> > Curious why/when you need such a function? Would the retrieval become
> > dependent on how the accessor is implemented, which would lead to that
> > the client code will rely on implementation details of API provider?
>
> It's mainly for debugging, but you can't have anything in the debug library
> (in fact, in any standard library) if it is not in the API.
>
> But I can think of a perfectly genuine non-debugging application too.
>
> A database may be implemented as a table, where each time new
> information is added, the old database is the __index of a new table
> containing the items that have just been added/updated and some
> fields identifying the update.
>
> When you retrieve an item, you would like to know its provenance.
> The "which" function directs you immediately to the source, or
> maybe to "SECRET".
>
> It does not rely on implementation details, only on the chronological
> ordering of updates.

Fair enough. If I understand correctly, in such an application, 'which' is equivalent to whether the value comes from the application cache or the actual data source. IMHO, you can have a different API, say, is_data_expired. I still feel the same way that asking which is equivalent to the object type in OO world, which has valid usage but disencouraged.