# How does nested tab completion work in the REPL?

**URL:** <https://discourse.julialang.org/t/how-does-nested-tab-completion-work-in-the-repl/102953>\
**Category:** General Usage\
**Tags:** repl, repl-autocomplete\
**Created:** [August 18, 2023, 1:20pm UTC](https://discourse.julialang.org/t/how-does-nested-tab-completion-work-in-the-repl/102953 "2023-08-18T13:20:51Z")\
**Posts on this page:** 1\
**Showing post:** 4

<div class="post-metadata">

**Author:** ![mkitti](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mkitti/32/12459_2.png) [@mkitti](https://discourse.julialang.org/u/mkitti)\
**Post date:** [August 18, 2023, 2:03pm UTC](https://discourse.julialang.org/t/how-does-nested-tab-completion-work-in-the-repl/102953/4 "2023-08-18T14:03:56Z")

</div>

Setup:

```julia
begin
    using HDF5, Downloads
    url = "https://github.com/evetion/SpaceLiDAR-artifacts/releases/download/v0.3.0/ATL08_20201121151145_08920913_006_01.h5";

    fn = Downloads.download(url, basename(url))
    h5f = h5open(fn)
end

begin
	 
   h5_to_tuple(h5o::Union{HDF5.File,HDF5.Group}) = 
    NamedTuple(Symbol.(keys(h5o)) .=> h5_to_tuple.(getindex.((h5o,), keys(h5o))))
    h5_to_tuple(h5o) = h5o
    nt = h5_to_tuple(h5f)
end

```

This works in the REPL:

```julia
julia> nt.[TAB]

METADATA ancillary_data ds_geosegments ds_metrics ds_surf_type gt1l gt1r
gt2l gt2r gt3l gt3r orbit_info quality_assessment
julia> nt.gt2l.[TAB]

land_segments signal_photons
julia> nt.gt2l.land_segments.[TAB]

asr atlas_pa beam_azimuth beam_coelev brightness_flag canopy cloud_flag_atm
cloud_fold_flag delta_time delta_time_beg delta_time_end dem_flag dem_h dem_removal_flag
h_dif_ref last_seg_extend latitude latitude_20m layer_flag longitude longitude_20m
msw_flag n_seg_ph night_flag ph_ndx_beg ph_removal_flag psf_flag rgt
sat_flag segment_id_beg segment_id_end segment_landcover segment_snowcover segment_watermask sigma_across
sigma_along sigma_atlas_land sigma_h sigma_topo snr solar_azimuth solar_elevation
surf_type terrain terrain_flg urban_flag
julia> nt.gt2l.land_segments.sat_flag.[TAB]

file id xfer
julia> nt.gt2l.land_segments.sat_flag
🔢 HDF5.Dataset: /gt2l/land_segments/sat_flag (file: ATL08_20201121151145_08920913_006_01.h5 xfer_mode: 0)
├─ 🏷️ DIMENSION_LIST
├─ 🏷️ _FillValue
├─ 🏷️ contentType
├─ 🏷️ coordinates
├─ 🏷️ description
├─ 🏷️ flag_meanings
├─ 🏷️ flag_values
├─ 🏷️ long_name
├─ 🏷️ source
├─ 🏷️ units
├─ 🏷️ valid_max
└─ 🏷️ valid_min

```

As in this issue:

> <https://github.com/JuliaIO/HDF5.jl/issues/1096>
>
> Is there a path to HDF5.jl supporting tab completion? It would be very powerful …for navigating opened h5 files but I'm guessing there is a good reason that it doesn't already exist.

This however does not work:

```julia
begin
	struct H5Indexer{O <: Union{HDF5.File,HDF5.Group}, C <: NamedTuple}
        parent::O
        children::C
	    function H5Indexer(p)
			pairs = Pair{Symbol,Any}[
				Symbol(k) => index(getindex(p,k))
				for k in keys(p)
			]
			#a = NamedTuple(Symbol(k) => v for (k,v) in attrs(p))
            #push!(pairs, :attrs => a)
            c = NamedTuple(pairs)
	    	new{typeof(p),typeof(c)}(p,c)
		end
	end
	index(h5o::Union{HDF5.File,HDF5.Group}) =
        H5Indexer(h5o)
    index(x) = x
	Base.parent(h5idx::H5Indexer) = getfield(h5idx, :parent)
	Base.getproperty(h5idx::H5Indexer, s::Symbol) =
		(@inline; getfield(getfield(h5idx, :children), s))
	Base.propertynames(h5idx::H5Indexer) =
        propertynames(getfield(h5idx, :children))
	Base.fieldnames(H5IDX::Type{H5Indexer{<: Any, C}}) where C =
		(@inline; fieldnames(C))
	Base.show(io::IO, m::MIME"text/plain", h5idx::H5Indexer) =
		show(io, m, getfield(h5idx, :parent))
end

```

I get the following behavior:

```julia
julia> h5idx.[TAB]                                     
METADATA ancillary_data ds_geosegments ds_metrics ds_surf_type gt1l gt1r gt2l gt2r gt3l gt3r orbit_info quality_assessment                                      
                                              
julia> h5idx.gt1r.[TAB]
# no suggestions 

```

What is special about a `NamedTuple`?

---

_[View the full topic](https://discourse.julialang.org/t/how-does-nested-tab-completion-work-in-the-repl/102953)._