Function repr::datum_list_size

pub fn datum_list_size<'a, I, D>(iter: I) -> usize where
    I: IntoIterator<Item = D>,
    D: Borrow<Datum<'a>>, 

Number of bytes required by a list of datums. This computes the size that would be required if the given datums were packed into a list.

This is used to optimistically pre-allocate buffers for packing rows.