Consider adding Bytes::try_mut() analog

[incidental-complexity]

In bytes 0.4.x, there was a method Bytes::try_mut() which would allow turning Bytes into (or back into) a BytesMut if it was the only pointer to the memory. This was good for allowing buffer reuse, as a buffer could be created as a BytesMut, updated, frozen to a Bytes, shared around, then recycled as a BytesMut again without having to do anymore allocation. This method pairs well with BytesMut::unsplit(), which allows this crate to be used as the basis of a fairly efficient buffer pool.

Bytes::try_mut() is gone now in 0.5.x.

The exact ergonomics aren't all that important (it could be a method on Bytes or a static method in BytesMut), but the functionality/semantics of being able to turn Bytes into a mutable was pretty useful. Can this be added back?

[TheButlah]

I am also curious about this, for the exact reason posted above. I had hoped that I could start out with BytesMut, build up my buffer, then freeze() it, pass it around, and once I was finished with it I could reclaim the memory with a try_mut() function to avoid reallocating.