allow passing multiple arguments to append! & prepend!

[rfourquet]

E.g. append!([1], [2], [3]) == [1, 2, 3].
The equivalent operations for sets (union!) and dictionaries (merge!)
already support multiple arguments, as well as push!.

For prepend!, order is maintained in the same way as in pushfirst!:
prepend!([3], [1], [2]) == [1, 2, 3] == pushfirst!([3], 1, 2).

[tkf]

LGTM

[Keno]

What's the rational for the prepend! behavior? Usually when the function modify their first argument, we have varargs behave as lfold.

[tkf]

append!(xs, a, b, c) is equivalent to push!(xs, a..., b..., c...). So, it makes sense if prepend!(xs, a, b, c) is equivalent to pushfirst!(xs, a..., b..., c...), as discussed in the OP.

It might make sense if pushfirst! had left-fold behavior but that's too late now.

[Keno]

Alright I buy that, but @StefanKarpinski or @JeffBezanson want to give a quick second opinion?

[StefanKarpinski]

Agree with what @tkf said, including the rationale and the potential regret.

[rfourquet]

News just added. As I think it's an uncontroversial change, I will merge soon.