Make type-construction more modular

See JuliaLang#8432 (comment)

base/multidimensional.jl

@@ -28,7 +28,7 @@ linearindexing(::Range) = LinearFast()
 abstract Subscripts{N} # the state for all multidimensional iterators
 abstract SizeIterator{N} # Iterator that visits the index associated with each element
 
-function gen_iterators(N::Int, with_shared=true)
+function gen_iterators(N::Int, with_shared=Base.is_unix(OS_NAME))
  # Create the types
  namestate = symbol("Subscripts_$N")
  namesize = symbol("SizeIterator_$N")
@@ -81,33 +81,35 @@ end
 done(R::StepRange, I::Subscripts{1}) = getfield(I, 1) > length(R)
 done(R::UnitRange, I::Subscripts{1}) = getfield(I, 1) > length(R)
 
-Base.start(A::AbstractArray) = start((A,linearindexing(A)))
+start(A::AbstractArray) = start((A,linearindexing(A)))
 start(::(AbstractArray,LinearFast)) = 1
 done{T,N}(A::AbstractArray{T,N}, I::Subscripts{N}) = getfield(I, N) > size(A, N)
 done{N}(iter::SizeIterator{N}, I::Subscripts{N}) = getfield(I, N) > getfield(iter.I, N)
 
 eachindex(A::AbstractArray) = eachindex(size(A))
 
 let implemented = IntSet()
-global eachindex
-global eachelement
-function eachindex{N}(t::NTuple{N,Int})
+global mditer_register
+function mditer_register(N::Int)
  if !in(N, implemented)
  eval(gen_iterators(N))
  end
+end
+end
+
+function eachindex{N}(t::NTuple{N,Int})
+ mditer_register(N)
  _eachindex(t)
 end
+
 function eachelement{T,N}(A::AbstractArray{T,N})
- if !in(N, implemented)
- eval(gen_iterators(N))
- end
+ mditer_register(N)
  A
 end
-end
 
 # Pre-generate for low dimensions
 for N = 1:8
- eval(gen_iterators(N, false))
+ eval(gen_iterators(N, false)) # SharedArray is not yet defined
  eval(:(eachindex(t::NTuple{$N,Int}) = _eachindex(t)))
  eval(:(eachelement{T}(A::AbstractArray{T,$N}) = A))
 end