Bug in lastindex/eachindex implementation for HDF5Dataset

[Luapulu]

julia> f
HDF5 data file: test.h5

julia> f["a"] = rand(100, 50)
100×50 Array{Float64,2}:
 0.260602  0.385837  0.866534   …  0.30788   0.0507932  0.260047
 0.891652  0.323088  0.0826012     0.722712  0.0977896  0.471532
 0.379407  0.450657  0.873643      0.564537  0.568046   0.884447
 0.365355  0.638885  0.64861       0.472992  0.786368   0.195252
 0.61823   0.484626  0.358584      0.392733  0.36302    0.608896
 0.717485  0.372161  0.710187   …  0.708059  0.923805   0.508474
 ⋮                              ⋱                       
 0.844055  0.142846  0.670188      0.220866  0.12411    0.78967
 0.713121  0.191025  0.876949   …  0.835709  0.905816   0.800183
 0.47358   0.559134  0.725292      0.176276  0.790019   0.100635
 0.644976  0.794425  0.388457      0.309014  0.653796   0.713121
 0.837234  0.688704  0.357377      0.870132  0.880849   0.716922
 0.253511  0.875848  0.922213      0.730818  0.539947   0.776605

julia> lastindex(f["a"])
5000

julia> f["a"][end]
ERROR: Wrong number of indices supplied, supplied length 1 but expected 2.
Stacktrace:
 [1] error(::String) at ./error.jl:33
 [2] hyperslab(::HDF5Dataset, ::Int64) at /Users/user/.julia/packages/HDF5/T1b9x/src/HDF5.jl:1854
 [3] _getindex(::HDF5Dataset, ::Type, ::Int64) at /Users/user/.julia/packages/HDF5/T1b9x/src/HDF5.jl:1775
 [4] _getindex(::HDF5Dataset, ::Int64) at /Users/user/.julia/packages/HDF5/T1b9x/src/HDF5.jl:1769
 [5] getindex(::HDF5Dataset, ::Int64) at /Users/user/.julia/packages/HDF5/T1b9x/src/HDF5.jl:1759
 [6] top-level scope at none:1

julia> eachindex(f["a"])
ERROR: MethodError: no method matching keys(::HDF5Dataset)
Closest candidates are:
  keys(::Cmd) at process.jl:639
  keys(::Core.SimpleVector) at essentials.jl:603
  keys(::BenchmarkGroup) at /Users/user/.julia/packages/BenchmarkTools/eCEpo/src/groups.jl:31
  ...
Stacktrace:
 [1] eachindex(::HDF5Dataset) at ./abstractarray.jl:209
 [2] top-level scope at none:1

lastindex and eachindex are both implemented using linear indexing, thus resulting in this error, since HDF5Datasets actually use cartesian indices. Shall I make a PR to redefine firstindex, lastindex and eachindex using cartesian indices? Or is there a function to read a HDF5Dataset at a given linear index?

[musm]

PRs are always welcome

[simonbyrne]

I think we should deprecate lastindex, since we don't support linear indexing.