Automatically save Dates

[willtebbutt]

It's doesn't presently appear possible to automatically save Date variables, as opposed to DateTime variables, but it's of course entirely possible that I'm mis-using the package. Specifically:

ds = Dataset("foo.nc", "c");

defDim(ds, "date", 250);

t = defVar(
    ds, "date", Int64, ("date", );
    attrib = Dict(
        "units" => "days since 1900-01-01 00:00:00.0",
        "long_name" => "date",
        "calendar" => "gregorian",
    ),
);

dates = range(Date(1905); step=Day(1), length=250);
t[:] = dates

yields

ERROR: MethodError: no method matching -(::Date, ::DateTimeStandard)
Closest candidates are:
  -(::Date, ::Day) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/Dates/src/arithmetic.jl:75
  -(::Date, ::Week) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/Dates/src/arithmetic.jl:73
  -(::Date, ::Month) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.5/Dates/src/arithmetic.jl:66
  ...
Stacktrace:
 [1] fromdate at /homes/wct23/.julia/packages/NCDatasets/eDnxY/src/cfvariable.jl:497 [inlined]
 [2] CFinvtransform at /homes/wct23/.julia/packages/NCDatasets/eDnxY/src/cfvariable.jl:517 [inlined]
 [3] macro expansion at /homes/wct23/.julia/packages/NCDatasets/eDnxY/src/cfvariable.jl:571 [inlined]
 [4] macro expansion at ./simdloop.jl:77 [inlined]
 [5] CFinvtransformdata at /homes/wct23/.julia/packages/NCDatasets/eDnxY/src/cfvariable.jl:570 [inlined]
 [6] setindex!(::NCDatasets.CFVariable{DateTime,1,NCDatasets.Variable{Int64,1,NCDataset},NCDatasets.Attributes{NCDataset{Nothing}},NamedTuple{(:fillvalue, :scale_factor, :add_offset, :calendar, :time_origin, :time_factor),Tuple{Nothing,Nothing,Nothing,String,DateTimeStandard,Int64}}}, ::StepRange{Date,Day}, ::Colon) at /homes/wct23/.julia/packages/NCDatasets/eDnxY/src/cfvariable.jl:624
 [7] top-level scope at REPL[120]:1

This workaround is fine for now:

t[:] = DateTime.(dates)

but perhaps it would be desirable to make it possible to do this conversion automatically? Or, if this functionality is intentional, so as to ensure that you get the same data types when loading a file back up, perhaps this workaround could be documented via some kind of error?

[willtebbutt]

I should add, I love the fact that this package automatically handles saving DateTimes -- it's really fantastic that that bit just works.

[visr]

See also #110, this can probably be closed in favor of that issue.

[willtebbutt]

Yup, can be closed in favour of that one.