Tricky to construct a dynamically sized ~[T]

[SiegeLord]

With the removal of ~[T] vector building functions by #13588, it is now very difficult to construct ~[T] with a size known at runtime. Currently I opted for this replacement of std::slice::from_elem:

fn from_elem<T: Clone>(size: uint, el: T) -> ~[T]
{
    use std::iter::Repeat;
    Repeat::new(el).take(size).collect()
}

but it is unclear to me if this workaround is not merely an oversight. Is the intention to make dynamically sized ~[T] impossible to construct?

[alexcrichton]

We have yet to provide a convenient conversion from Vec<T> to ~[T], but one will be provided. Your example would look like:

let foo: ~[T] = Vec::from_elem(n, e).insert_method_name_here();

Currently insert_method_name_here() is move_iter().collect().

[gereeter]

Even assuming proper conversion from Vec<T> to ~[T], I think this brings up a valid point. slice::from_fn and slice::from_elem are not in anyway problematic with DST as they are provided a length at runtime. All the other functions removed in #13588 have to do with growing and shrinking, but from_fn and from_elem do not. It seems perfectly reasonable to reinstate them.

[thestinger]

The ~[T] type has been removed.

[SiegeLord]

It's tricky to construct a dynamically sized Box<[T]> too, so it seems this is still valid... but w/e.