Both the name of and the docs for MaybeUninit::uninit_array() make what it actually does somewhat unclear

[slightlyoutofphase]

Basically, based on the name of the function, and also the part of the docs for it that says:

Create a new array of MaybeUninit<T> items, in an uninitialized state.

I initially had the impression that it internally amounted to:

MaybeUninit::<[MaybeUninit<T>; LEN]>::uninit()

and returned an uninitialized array of uninitialized MaybeUninits.

However, after looking at the source, I realized it actually amounts to:

MaybeUninit::<[MaybeUninit<T>; LEN]>::uninit().assume_init()

and returns an initialized array of uninitialized MaybeUninits (which is what I actually needed, so that's good at least!)

[hkBst]

IIUC you assumed MaybeUninit<[MaybeUninit<T>; N]> as output, but the documented output is [MaybeUninit<T>; N]. I don't think MaybeUninit<[MaybeUninit<T>; N]> is a useful type as an array really is nothing more than its elements, so if those are uninitialized, then the array is already uninitialized as a whole, since there is nothing else besides the elements.

Maybe the "in an uninitialized state" is ambiguous as to whether it refers to the array or the elements though.

[RalfJung]

However, after looking at the source,

You don't have to look at the source for that, the type is right there in the docs. :)