library(data.table)
# desired solution
a <- data.table(c1 = 1, c2 = 'asd', c3 = expression(as.character(Sys.time())))
b <- data.table(c1 = 3, c2 = 'qwe', c3 = expression(as.character(Sys.time()+5)))
dt <- rbind(a,b)
#Error in rbindlist(allargs) : Unsupported column type 'expression'
dt <- rbindlist(list(a,b))
#Error in rbindlist(list(a, b)) : Unsupported column type 'expression'

# current workaround
a <- data.table(c1 = 1, c2 = 'asd', c3 =
list(expression(as.character(Sys.time()))))
b <- data.table(c1 = 3, c2 = 'qwe', c3 =
list(expression(as.character(Sys.time()+5))))
dt <- rbind(a,b)
dt <- rbindlist(list(a,b))
# both ok, but the desired solution would be:
dt[,list(c1,c2,eval(c3))]
# and it will not produce expected results because of previous workaround
# another workaround must be done:
dt[,list(c1,c2,lapply(c3,eval))]