no way to mutate contents of stack (and presumably other containers)

[andrewcooke]

this should illustrate the issue:

julia> s = Stack(Int)
DataStructures.Stack{DataStructures.Deque{Int64}}(Deque [Int64[]])

julia> push!(s, 0)
DataStructures.Stack{DataStructures.Deque{Int64}}(Deque [[0]])

julia> top(s) += 1
ERROR: syntax: invalid assignment location

julia> a = Array(Int, 0)
0-element Array{Int64,1}

julia> push!(a, 1)
1-element Array{Int64,1}:
 1

julia> a[end] += 1
2

julia> a
1-element Array{Int64,1}:
 2

not pressing - going to switch to arrays instead of stacks.

[oxinabox]

I don't think this is actually possible. If julia had have evolved in a different direction in 2015 it might have been. But right now primitive types are immutable, and thus functions whos return values are immuatble, can not be used as targets to mutate their source.

If a mutable value is used then it is fine:

julia> t = Stack(Ref{Int})
DataStructures.Stack{Ref{Int64}}(Deque [Ref{Int64}[]])

julia> b=Ref(1)
Base.RefValue{Int64}(1)

julia> push!(t,b)
DataStructures.Stack{Ref{Int64}}(Deque [Ref{Int64}[Base.RefValue{Int64}(1)]])

julia> top(t)[]+=3
4

julia> top(t)
Base.RefValue{Int64}(4)

I guess one could overload setindex for Dequeues, but right now we don't even overload getindex.

[oxinabox]

Closing for now. if it comes up, feel free to open a new issue for setindex or getindex I am undecided if we should have them