Slicing an ArrayView restricts lifetime

[cassiersg]

The following doesn't work, due to the signature of ArrayBase::slice.

fn foo<'a>(x: ArrayView1<'a, i32>) -> ArrayView<'a, i32> {
    x.slice(s![1..])
}

It would be nice to have a method dedicated to this on ArrayView, similarly to ArrayView::to_slice, (which is a taylor-adapted version of ArrayBase::as_slice).

[jturner314]

The slice_move method on ArrayBase can be used for this purpose. If you don't want to lose access to the original view, note that const-ndim ArrayViews implement Copy and Clone, and dynamic-ndim ArrayViews implement Clone. However, I'm not opposed to adding a special method to ArrayView if we can come up with a good name for it, since there is a potential efficiency gain from a specialized implementation instead of .clone().slice_move().

[cassiersg]

Thank you, I missed slice_move. I'll go with that. I guess overhead of .clone().slice_move() will be negligible except in rather rare situations.

[jturner314]

Yeah, for ArrayView1 especially, you don't even need the .clone() since it implements Copy, and the overhead relative to a specialized method should be zero or negligible.

[cassiersg]

I opened #989 which would have helped me not miss the .clone().slice_move() solution. Re-perf: indeed, and also for any dimensionality as long as you deal with large matrices (and actually do something with them).

Leaving up to you to close this or not.

[jturner314]

Okay, I'll go ahead and close this.

To anyone coming across this issue: If .clone().slice_move() isn't good enough, and you need a method

impl<'a, A, D> ArrayView<'a, A, D> {
    fn foo<I>(&self, info: I) -> ArrayView<'a, A, I::OutDim> 
    where
        I: SliceArg<D>,
    { ... }
}

and have a good name for it, please feel free to reopen this issue or create a new one referencing it.