Fix last label

[ogauthe]

This PR fixes a lost label in last. The lost label triggered a type unstability which is now fixed. However, I have not been able to add a test for this case. No function allows to create an AbstractUnitRange with empty lasts. It can still be initialized explicitly, but it has many issues (first crashes), preventing testing.

Maybe we should just return last(a.lasts) and accept a crash for empty a.lasts (which is still the current behavior)?

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[mtfishman]

However, I have not been able to add a test for this case. No function allows to create an AbstractUnitRange with empty lasts. It can still be initialized explicitly, but it has many issues (first crashes), preventing testing.

Here is one way to construct it:

julia> r = gradedrange(Pair{String,Int}[])
GradedUnitRanges.GradedOneTo{LabelledNumbers.LabelledInteger{Int64, String}, Vector{LabelledNumbers.LabelledInteger{Int64, String}}}

but as you pointed out I see that first(r) crashes. I think it isn't well defined since we haven't specified the label (it should output a labelled 1 value following the convention of BlockArrays.AbstractBlockedUnitRange), maybe we should support:

julia> r = gradedrange("x" => 1, Pair{String,Int}[])

julia> r = gradedrange("x", Pair{String,Int}[]) # If only the label is specified, assume the value starts at 1

to allow specifying the first value/label (not saying we need to do that in this PR, I'm just trying to put this issue into a bigger context).

Maybe we should just return last(a.lasts) and accept a crash for empty a.lasts (which is still the current behavior)?

The current code matches the behavior of last(::AbstractBlockedUnitRange):

julia> using BlockArrays

julia> first(blockedrange(1, Int[]))
1

julia> last(blockedrange(1, Int[]))
0

julia> first(blockedrange(Int[]))
1

julia> last(blockedrange(Int[]))
0

which follows from Julia's definition for empty ranges:

julia> first(1:0)
1

julia> last(1:0)
0

so I think it makes sense as it is, with your new improvements.

[ogauthe]

We could indeed allow for r = gradedrange("x", Pair{String,Int}[]) , although I would wait for a use case before implementing it. So I am fine with merging the code as it is, I just bumped the version according to #5