Compatibility with older versions of boost

[MichaelChirico]

Hi, we are stuck with an old (1.67) version of boost. I was able to get colourvalues working (compiles and passes tests) by making pretty minor edits here:

https://github.com/SymbolixAU/colourvalues/blob/1236cbd8cf80f450f72ae229f5be3124de4fc9bd/inst/include/cardinal_cubic_b_spline.hpp#L25

It was straightforward to swap out cardinal_cubic_b_spline_detail.hpp for cubic_b_spline_detail.hpp. Is there any known impact on behavior from doing so? It should also be relatively easy to have an #ifdef block to use the right header depending on the version.

[dcooley]

I don't think I can confirm one way or another what the impact will be if I'm honest, as I don't know the differences between the implementations. I can't imagine it will be noticable from an end-user perspective though.

I'm happy if you want to make a PR with the #ifdef so it works for you.

[MichaelChirico]

I did see this in the original commit for the cardinal_ version:

https://github.com/boostorg/math/commit/caf1883788da6fcbfd293e805806b312e595963a

(but I also can't make heads or tails of it). Such a PR would be great! I've edited our local copy to work, but would be helpful for others (?) that might be stuck with old boost to get colourvalues working.