Make append! and push! definitions more generic

[nalimilan]

Some methods for append! and push! for Array actually work for any AbstractArray since they only use resize!, setindex! and push!. Broaden the signatures so that custom array types do not need to copy definitions from Base.

BitArray uses special methods, one of which was apparently not covered by tests.

Ideally, fallback append!(::AbstractVector, ::AbstractVector) and push!(::AbstractVector, ::Any) methods would also be provided. Unfortunately, the existing definitions for Vector call _grow_end instead of resize!, which means that simply broadening the signature to AbstractVector won't work. It would be easy to fix that (using x isa Vector or a helper function), but since the non-Vector code path would not be used in Base I'm not sure that's OK. Comments?

[timholy]

Should the necessary methods be added to the interfaces chapter? Perhaps on a section on growable arrays?

It would be easy to fix that (using x isa Vector or a helper function), but since the non-Vector code path would not be used in Base I'm not sure that's OK. Comments?

There is a precedent: Base doesn't export an OffsetArray type yet we have a bunch of tests that exercise that functionality.

[nalimilan]

Should the necessary methods be added to the interfaces chapter? Perhaps on a section on growable arrays?

Yes, that would be useful. There are other similar functions to list (like insert!, splice!, prepend! and pop!). Why not just add a new section in the existing table about the AbstractArray interface? It already has sections.

But I'd first want to tackle the question of whether we can provide generic implementations for these.

There is a precedent: Base doesn't export an OffsetArray type yet we have a bunch of tests that exercise that functionality.

So basically you say it would be OK to replace _growend!(a, n) with a isa Vector ? _growend!(a, n) : resize!(a, length(a)+n) even if that's not used directly by Base?

[JeffBezanson]

It's not clear to me whether the method for append!(::Vector, ::AbstractVector) is even any better than the method for append!(::AbstractVector, ::Any).

[nalimilan]

Ah, indeed, so maybe this PR is all we need actually. Cool.