[a;b] is a bit regressed now when it comes to type stability, see: https://github.com/JuliaLang/julia/issues/13254
On Monday, October 19, 2015 at 4:56:40 PM UTC+2, Josh Langsfeld wrote: > > [a; b] / vcat(...) is type stable. It may produce different output > depending on the types of a and b but it won't change behavior depending on > their values. > > On Monday, October 19, 2015 at 10:20:06 AM UTC-4, Andras Niedermayer wrote: >> >> In light of the recent discussions ( >> https://groups.google.com/forum/#!topic/julia-users/xJ7GpKAa16E and >> https://groups.google.com/forum/#!topic/julia-users/_lIVpV0e_WI) I got >> curious, whether there is a non-modifying version of push!, since >> push!(copy(a),b) doesn't feel right (I try to avoid modifying functions, >> except if I really need performance) and [a; b] is not type stable: >> >> f(a) = [a; 3] >> f2(a) = push!(copy(a),3) >> >> >> julia> Base.return_types(f,(Array{Int64,1},)) >> 1-element Array{Any,1}: >> Array{T,N} >> >> >> julia> Base.return_types(f2,(Array{Int64,1},)) >> 1-element Array{Any,1}: >> Array{Int64,1} >> >> >> I couldn't find anything in the Julia docs. Of course, I could just >> define my own >> >> push(a,vars...) = push!(copy(a),vars...) >> >> >> but if there is a standard way to do that, I'd prefer that. Maybe there's >> also some clever way to avoid making a copy if `a` is a literal (e.g. >> push([1,2]) >> ). >> >> The same applies to unshift, etc. >> >> (Non-modifying `shift!` and `pop!` already exist with the names `first` >> and `last`. I'd find it easier to remember `shift` and `pop` -- it would >> also be more similar to `merge` vs `merge!` for dictionaries, but I guess >> that's just my taste.) >> >
