Some issue with similar

[davidanthoff]

@JeffBezanson reports this over at JuliaData/Missings.jl#6 (comment):

It works pretty well, but I ran into the issue recently that similar(a::DataValueArray, Any) does not return an array that can hold any value, which prevents Base map and collect from working.

@JeffBezanson: do you have a little more info what you were trying to do?

The following seems to work:

using DataValues

x = DataValueArray([1,2,NA])

y = similar(x, Any)
y[1]="asdf"
y[2]=3.5

The type of y is DataValues.DataValueArray{Any,1}, and now that I think about it, maybe it should just be Array{Any,1}, right? But things shouldn't break, regardless of that specific choice.

[JeffBezanson]

The problem is that the eltype of similar(a::DataValueArray, Any) is not Any but DataValue{Any}, so the logic in e.g. map copies the array on every iteration thinking the type is not wide enough yet.

[davidanthoff]

Yeah, that is just a bug. #33 changes this so that similar only returns a DataValueArray when you pass DataValue as the desired element type. That seems more sensible. I just hope I'm not introducing some method ambiguity with this new definition... They always make me nervous. If you spot some problem there, please let me know!