Added [<-.IDate so that rbind.data.frame retains integer IDate

[MichaelChirico]

Closes #2008

I still don't really understand why these changes are necessary (and both are in fact necessary).

I posted this on r-devel, might be some insight there: https://stat.ethz.ch/pipermail/r-devel/2019-May/077866.html

[MichaelChirico]

Josh Ulrich replied on r-devel, misunderstanding was pretty simple -- [<- is called by rbind.data.frame. Meanwhile [<-.Date does a funny thing where it retains its class while also calling as.Date, which converts to numeric.

So the approach here seems correct.

[MichaelChirico]

Wow, the level of deja vu on reading this:

It seems that the .Internal rbind of two data.frame coerces IDate to numeric. Tried defining "[<-.IDate" as per Tom's suggestion, and c.IDate to no avail (maybe because the .Internal code in bind.c doesn't look up package methods?)

In fact I went through the same existential crisis for a while this morning! I'm not sure what was tried for [<-.IDate back then, maybe the NextMethod approach? I tried that as well but it seems fundamentally doomed because ... in NextMethod can't be passed as origin to the as.Date call in [<-.Date, which is needed if we pass the underlying integer to [<-.Date as value. If we pass an IDate, the #2008 problem happens -- double with IDate class. I didn't try running as.Date(value) but that would mean coercing numeric just to get [<-.Date and then back to integer aftewards... seems silly.

Anyway I think we can change this test that was testing that a bug was still a bug. Now the bug is fixed. I'm not sure if the subsequent test is still needed, but it can't hurt.

[codecov]

Codecov Report

Merging #3602 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #3602      +/-   ##
==========================================
+ Coverage   97.81%   97.81%   +<.01%     
==========================================
  Files          66       66              
  Lines       12909    12915       +6     
==========================================
+ Hits        12627    12633       +6     
  Misses        282      282

Impacted Files	Coverage Δ
R/IDateTime.R	98.75% <100%> (+0.04%)	⬆️

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