implicit re-casting of logical to Date fails

[MPagel]

using data.table 1.14.0 built under R version 3.6.3 in RStudio Version 1.1.463 session using R version 3.6.0

slightly modified and greatly expanded from https://stackoverflow.com/a/54081089/4228193

using
alldata <- data.table(1)[,:=(c("va", "vb", "vc", "vd"),NA)][,V1:=NULL][.0]
or
alldata <- data.table(1)[,:=(c("va", "vb", "vc", "vd"),NA)][,V1:=NULL][!is.na(va)]

creates an empty data.table with 4 named columns, which I intend to iteratively append to with the results of an fread (stored in filedata). You can dummy up a value for filedata with filedata <- data.table(1)[,:=(va="bob", vb="barbara ann", vc=4, vd=as.Date("1965-09-23"), V1=NULL)]

alldata[,lapply(.SD,class)] # 0-row data seeded with NA in each column

    va      vb      vc       vd

1: logical logical logical logical

filedata[,lapply(.SD,class)] # lines of real data that you are trying to merge

      va        vb      vc   vd

1: character character integer Date

rbindlist(list(alldata,filedata))

Error in rbindlist(list(alldata, filedata), use.names = FALSE) :
Class attribute on column 4 of item 2 does not match with column 4 of item 1.

Basically, a logical column can't be auto-recast to a Date data type. Nor is IDate class data allowed to be appended to the vd column of filedata (code and results not shown here).

the Date class itself appears to accept NA as a value, but this NA appears to be slightly different from a logical NA
filedata <- data.table(1)[,:=(va="bob", vb="barbara ann", vc=4, vd=as.Date(NA))][,V1:=NULL]
filedata

va vb vc vd
1: bob barbara ann 4 <NA>

filedata[,lapply(.SD, class)]

      va        vb      vc   vd

1: character character numeric Date

rbindlist(list(alldata,filedata))

Error in rbindlist(list(alldata, filedata)) :
Class attribute on column 4 of item 2 does not match with column 4 of item 1.

filedata <- data.table(1)[,:=(va="bob", vb="barbara ann", vc=4, vd=as.logical(NA))][,V1:=NULL]
filedata[,lapply(.SD, class)]

      va        vb      vc      vd

1: character character numeric logical

rbindlist(list(alldata,filedata)) # note the lack of <> brackets around NA

va          vb vc vd

1: bob barbara ann 4 NA

...but it seems you can convert from a logical to a Date with explicit casting outside of data.table...
as.integer(as.logical(NA))

[1] NA

as.character(as.logical(NA))

[1] NA

as.Date(as.logical(NA))

[1] NA

class(as.Date(as.logical(NA)))

[1] "Date"

[avimallu]

Related #5309, and probably original known from #3911.

ReprEx:

library(data.table)
DT1 = data.table(NA)
DT2 = data.table(as.Date(NA))
rbindlist(list(DT1, DT2))

[MPagel]

Please mark as a duplicate or supplementary to #3911