Re: [gentoo-python] [python-r1] Getter functions or 'export' function?

[Mike Gilbert]

On Sun, Oct 21, 2012 at 5:16 AM, Michał Górny <mgorny@g.o> wrote:
> Hello,
>
> Right now, there are two variables which are set per-implementation --
> PYTHON & EPYTHON. However, one of our users (sorry for not remembering
> who) requested an ability to get Python libdir, site-packages directory
> as well. This raises a question on the interface which should be used
> to get those values.
>
> The common interface in Gentoo is to use 'getter' functions. Since bash
> doesn't have any real concept of return values, those functions use
> output capturing -- and that involves subshelling which is pretty bad
> for commonly used functions. An alternative is to use an 'export'
> function like tc-export() in toolchain-funcs.
>
> I'd like to shortly point out advantages and disadvantages of each
> solution.
>
>
> 1) getter functions
>    - python_get_PYTHON [<impl>]
>    - python_get_EPYTHON <impl>
>    - python_get_sitedir [<impl>]
>
> + clear separation between variables
>   -> especially useful to keep docs clear and short
>
> - one subshell (and function call) for each variable, for each
>   implementation
>   -> that makes it 2 * n-impls for each phase function in distutils-r1
>
>
> 2) a single export function
>    - python_export [<impl>] <var>...
>    e.g. python_export python2_7 PYTHON EPYTHON PYTHON_SITEDIR
>
> + no subshelling
>
> + multiple variables can be set in a single function call
>
> - potential for variable conflicts
>   -> e.g. when PYTHON_SITEDIR is used differently by the build system,
>      the ebuild would need to 'move' it (unlikely but possible)
>
> - mixing of implementation and variables in parameters (optional first
>   parameter)
>   -> technically it's acceptable but looks a bit bad.
>
>
> What are your thoughts?
>

I think creating sub-shells in sections which are not processed in
global scope is really not a big deal.

I think the getter functions are more intuitive. However, I also like
the idea of setting variables at the same time, similar to the way
this is handled in _tc-getPROG. The result is stored in a variable and
also echoed, leaving it up to the end user to decide how he wants to
process it.

So, I vote for getters that emulate the toolchain-funcs behavior.