Should `BlockRngCore::Results` also be `AsMut`?

[pitdicker]

I think adding the bound now is no big deal, and it could allow for a BlockRng-like implementation that zeros out used results.

On the other hand I don't see much value in modifying / using Results from the 'outside'. Anything that can read the results field of BlockRng can probably also read the internal state of the RNG, so why take extra precautions?

[dhardy]

I guess that sounds okay. In any case, BlockRng (or other Rng impl) can govern access to the results field.

[dhardy]

Done: #419