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On 09/08/2010 03:03 PM, Michał Górny wrote:
> Hello,
>
> We already have a variety of use_*() functions with their specific
> uses. But what I miss is a single, simple and universal use_echo()
> function, behaving similarly to ?: operator in C. In other words, a
> simple function replacing monsters like:
> $(use foo && echo bar || echo baz)
>
> Such a function could be implemented inside eutils eclass. The synopsis
> could be:
> use_echo use1 [val1 [use2 val2 [...]] [otherwise]]
>
> The idea is to echo 'valN' if 'useN' flag applies, or 'otherwise' if
> none of them do. If called with a single arg, it would assume
> val1=use1. If called with an even number of args (i.e. no 'otherwise'),
> it would not output anything if none of the flags match.
>
> For example, the code recalled above could be then rewritten as:
> $(use_echo foo bar baz)
>
> The multi-argument version could be used with one-of cases like:
> GUI=$(use_echo gtk GTK2 qt4 QT4 NONE)
> (for games-emulation/mupen64plus).
>
> The resulting function would certainly find use in packages using plain
> make. For an example, in net-misc/autoupnp (sunrise overlay) I use:
> WANT_LIBNOTIFY=$(use libnotify && echo true || echo false)
> That would be much shorter as:
> WANT_LIBNOTIFY=$(use_echo libnotify true false)
>
> The function could be used to reimplement some of use_*() functions
> within other eclasses too.
>
Just as a proof-of-concept, here's one implementation of such a
function, allowing for an arbitrary number of arguments:
use_echo() {
while [[ $# -gt 1 ]]; do
if use "$1"; then
echo "$2"
return
fi
shift 2
done
[[ $# -eq 1 ]] && echo "$1"
}
- --
Jonathan Callen
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