Outdated document for truelength

[rajkrpan]

To quote help("truelength"):
For tables loaded from disk however, truelength is 0 in R 2.14.0 and random in R <= 2.13.2; i.e., in both cases perhaps unexpected. data.table detects this state and over-allocates the loaded data.table when the next column addition or deletion occurs. All other operations on data.table (such as fast grouping and joins) do not need truelength.
It seems that the documentation is out of date since the copy doesn't happen during deletion of a column. Check http://stackoverflow.com/questions/35362336/why-does-data-table-get-copied-when-adding-a-new-column/35362681#35362618 for further info.