Repository navigation
ArrayViewMut::into_view() should be public #1595
Description
There is no public API to convert an owned ArrayViewMut<'a, T, D> to ArrayView<'a, T, D> while preserving the original lifetime 'a. The method into_view() exists internally but is pub(crate).
ArrayViewMut has a .view() method, but it cannot be used here because its signature borrows self. A simplified example of my use case where I have an ArrayViewMut inside a struct:
use ndarray::{ArrayView2, ArrayViewMut2};
struct Foo<'a> {
data: ArrayViewMut2<'a, f32>,
}
impl<'a> Foo<'a> {
/// Downgrade to a shared view. This fails to compile.
fn into_shared(self) -> ArrayView2<'a, f32> {
self.data.view() // error[E0515]: returns value referencing local `self.data`
}
}The compiler complains:
error[E0515]: cannot return value referencing local data `self.data`
--> src/main.rs:10:9
|
10 | self.data.view()
| ^^^^^^^^^------
| | |
| | `self.data` is borrowed here
| returns a value referencing data owned by the current function
The data pointed to by self.data is valid for 'a, but .view() can only express "valid for the duration of the &self.data borrow", which expires when self is dropped at the end of into_shared. The internal ArrayViewMut::into_view(self) -> ArrayView<'a, A, D> handles this correctly but is pub(crate).
I can work around this with unsafe { std::mem::transmute(...) } as a workaround which is valid but gross.
Request
Make into_view(self) -> ArrayView<'a, A, D> public, or add a From<ArrayViewMut<'a, A, D>> for ArrayView<'a, A, D> impl.
Activity
cschanhniem commentedon Jun 19, 2026
Confirmed on
master—src/impl_views/conversions.rsline:The fix is a one-line change: make it
pubinstead ofpub(crate). The method is already well-exercised internally — it's used byinto_outer_iter,into_axis_iter,into_axis_chunks_iter,into_indexed_iter, and the variousinto_*_mutmethods all chain through it. This gives confidence it won't break anything.An alternative (or addition) would be a
Fromimpl:That would let users write
let shared: ArrayView<'_, _> = mut_view.into();directly. Happy to submit a PR with either approach (or both).jiawen commentedon Jun 19, 2026
Amazing, thank you!