Immutable vs Type: reassignment via arrays and performance

General Usage
7

Doesn’t seem to work:

ERROR: MethodError: no method matching +(::Void, ::Void)
Closest candidates are:
  +(::Any, ::Any, ::Any, ::Any...) at operators.jl:138
 in mapfoldl_impl(::Base.#identity, ::Base.#+, ::Void, ::Base.Generator{Array{ArrFloat,1},##36#38}, ::Int64) at .\reduce.jl:46```