Instead of lengthy blurbs, switch to single-line, machine-readable
standardized (https://spdx.dev) license identifiers. The Linux kernel
switched long ago, so there is strong precedent.
Three cases are handled: AGPL-only, Apache-only, and dual licensed.
For the latter case, I chose (AGPL-3.0-or-later and Apache-2.0),
reasoning that our changes are extensive enough to apply our license.
The changes we applied mechanically with a script, except to
licenses/README.md.
Closes#9937
Convert tri_comparators to return std::strong_ordering rather than int,
to prevent confusion with less comparators. Downstream users are either
also converted, or adjust the return type back to int, whichever happens
to be simpler; in all cases the change it trivial.
The motivation for supporting ring position is that containers using
it can be self sufficient. The existing compatible_ring_position_view
could lead to use after free when the ring position data, it was built
from, is gone.
The motivation for compatible_ring_position_or_view is to allow lookup
on containers that don't support different key types using c__r__p,
and also to avoid unnecessary copies.
If the user is provided only with a ring_position_view, c__r__p__or_v
could be built from it and used for lookups.
Converting ring_position_view to ring_position is very bug prone because
there could be information lost in the process.
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
compatible_ring_position's sole purpose is to allow creating
boost::icl::interval_map with dht::ring_position as the key and list of
sstables as the value. This function is served equally well if
compatible_ring_position wraps a `dht::ring_position_view` instead of a
`dht::ring_position` with the added benefit of not having to copy the
possibly heavy `dht::decorated_key` around. It also makes it possible
to do lookups with `dht::ring_position_view` which is much more
versatile and allows avoiding copies just to make lookups.
The only downside is that `dht::ring_position_view` requires the
lifetime of the "viewed" object to be taken care of. This is not a
concern however, as so long as an interval is present in the map the
represented sstable is guaranteed to be alive to, as the interval map
participates in the ownership of the stored sstables.
Rename compatible_ring_position to compatible_ring_position_view to
reflect the changes.
While at it upgrade the std::experimental::optional to std::optional.
ring_position is built for modern code that does not require default
constructors or stateless comparators. But not all code is modern, so
supply a compatible_ring_position that works with old code, at the cost
of some extra storage. Intended user is boost's interval container
library.
