Function pre_compute_object_size 

pub fn pre_compute_object_size<'a, V, I>(
    entries: I,
    options: &Options,
    sizes: &mut Vec<Size>,
) -> Size
where
    I: IntoIterator<Item = (&'a str, V)>,
    V: PrecomputeSize,

Computes the printed size of an object made of entries.