License incompatibility with TBB

[wds15]

The Intel TBB is licencsed under the Apache 2.0 licence. According to the FOSS, this license is only compatible with GPL-3 while it is not compatible with earlier versions of the GPL. Please refer to the homepage from the GNU project for their view on the Apache 2.0. There they explicitly list that the GPL-2 is incompatible with the Apache 2.0 license. Currently, RcppParallel is released under the GPL-2 and an update to GPL-3 should be considered, I think.

[eddelbuettel]

Thanks, probably something we should do.

[wds15]

Sure... NP. I hope that's an easy thing to do.

[kevinushey]

Sorry for the delay; I've finally made this change with 577c920.