Provide a method to allocate a slice of zeroed/default values

[ztlpn]

Currently to bump-allocate any slice an existing slice is needed which is not always convenient. I guess currently the workaround is to use the alloc_layout method, but a method that doesn't require unsafe would be handy. Another handy addition would be a method that allocates and fills a slice with copies/clones of a single value.

[ztlpn]

@fitzgen I can do a PR if you think that this addition makes sense.

[fitzgen]

Can you sketch the API / method signature you're looking for here?

Zeroing memory is not going to result in a safe API in the general case (hence std::mem::zeroed being unsafe) so if your goal is avoiding unsafe I think we might need to workshop the API design a bit.

[ztlpn]

Something like

fn alloc_slice_fill_copy<T: Copy>(&self, len: usize, value: &T) -> &mut [T];
fn alloc_slice_fill_clone<T: Clone>(&self, len: usize, value: &T) -> &mut [T];
fn alloc_slice_fill_default<T: Default>(&self, len: usize) -> &mut [T];

Basically the equivalent of vec![len; value].

Zeroing memory is not going to result in a safe API in the general case

Yeah, I don't need zeroed memory in particular, but slice with default values. It was just that I had integer types in mind when I created the issue.

[fitzgen]

That looks great -- happy to take a PR implementing those APIs!

[fitzgen]

I believe this is fully implemted now. If I'm mistaken, please re-open!

[ztlpn]

Thanks! @fitzgen It would be great if you could cut a release with this feature!

[fitzgen]

See #51