>>>>> On Mon, 2 Feb 2015, Alexis Ballier wrote: > Ulrich Mueller <[email protected]> wrote:
>> In a nutshell, you have a binary choice here, namely ffmpeg or >> libav as implementation, and instead of one USE flag you want to >> introduce two (ffmpeg_impl_ffmpeg and ffmpeg_impl_libav), but of >> the 4 possible combinations only 2 are valid. So you need a >> REQUIRED_USE to forbid some combinations. > We already have three possibilities: ffmpeg, libav or none (only for > some packages but they do exist). Right. > With the N-1th proposal, it was overseen that USE="-ffmpeg libav" > should be forbidden by REQUIRED_USE. Why? When you have USE="-ffmpeg", the libav flag is a "don't care" which is ignored. "ffmpeg" controls the feature, "libav" chooses the implementation. This is very clear from the flags' descriptions and was also well explained in the (N-1) news item. -ffmpeg -libav -> none -ffmpeg +libav -> none +ffmpeg -libav -> ffmpeg +ffmpeg +libav -> libav > With the N-1th proposal, we had two bits (USE='ffmpeg libav') to > code 3 states. With the above proposal, we have a kind of unary > coding: USE=-ffmpeg means 'none', USE=ffmpeg + ffmpeg_impl_$x means > '$x'. Yes, but you would then have 3 bits (i.e. 8 combinations) to code only 3 possible states. > I understand your point; I'm not entirely convinced which one is > better, but I'm tempted by the simplicity for users of the above > unary proposal. Ulrich
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