Define some modifying functions for OffsetVector

[fredrikekre]

I had these in my own code, might as well upstream them.

[timholy]

push! and pop! seem fine. With pushfirst!/popfirst!, my worry is that the natural thing to do would be to mutate the initial index, but we can't do that without making the wrapper mutable. (See https://github.com/JuliaArrays/CatIndices.jl/blob/master/src/bidirectional.jl.) If we accepted those and then someday got an API for mutating immutables and then decide we want to change how pushfirst! works, it becomes non-deprecatable breaking behavior. Of course we could do that (e.g., OffsetArrays v2.0.0), so that's not a killer argument. Nevertheless, I'm tempted to leave those out of this. Thoughts?

[fredrikekre]

With pushfirst!/popfirst!, my worry is that the natural thing to do would be to mutate the initial index

Okay, that is not what pushfirst!(::Vector) does though?

[timholy]

Right, pushfirst! on a vector does not mutate the initial index. So we could say that this is just how pushfirst! works. I could agree to that.

OTOH Vector lies in that fuzzy world spanning both views of 1-d arrays, either "I'm just a list of elements" or "I'm an associative container with integer keys." pushfirst! seems to belong to the first world, but most uses of OffsetArrays are probably in that second world.

[fredrikekre]

Alright, I dropped (push|pop)first! for now at least.

[fredrikekre]

bump.