Base.getindex not implemented for Attribute type

[david-macmahon]

The only way I can see to get the value of an Attribute is through read(attr). I'd like to be able to use the Dataset-like way of accessing the value of an Attribute via the Base.getindex function (i.e. by using attr[] instead of read(attr)).

I see that src/HDF5.jl defines Base.getindex(dset::Dataset, I...), but the neighboring functions operate on a DatasetOrAttribute Union type. I can't find any comments in the code or in commit log messages that explain why this function is limited to just the Dataset type rather than the broader DatasetOrAttribute type.

The generic_read function used by getindex already operates on DatasetOrAttribute, which suggest that it's just an oversight, but is there some reason for restricting getindex to just Dataset types?