in C++20, compiler generate operator!=() if the corresponding
operator==() is already defined, the language now understands
that the comparison is symmetric in the new standard.
fortunately, our operator!=() is always equivalent to
`! operator==()`, this matches the behavior of the default
generated operator!=(). so, in this change, all `operator!=`
are removed.
in addition to the defaulted operator!=, C++20 also brings to us
the defaulted operator==() -- it is able to generated the
operator==() if the member-wise lexicographical comparison.
under some circumstances, this is exactly what we need. so,
in this change, if the operator==() is also implemented as
a lexicographical comparison of all memeber variables of the
class/struct in question, it is implemented using the default
generated one by removing its body and mark the function as
`default`. moreover, if the class happen to have other comparison
operators which are implemented using lexicographical comparison,
the default generated `operator<=>` is used in place of
the defaulted `operator==`.
sometimes, we fail to mark the operator== with the `const`
specifier, in this change, to fulfil the need of C++ standard,
and to be more correct, the `const` specifier is added.
also, to generate the defaulted operator==, the operand should
be `const class_name&`, but it is not always the case, in the
class of `version`, we use `version` as the parameter type, to
fulfill the need of the C++ standard, the parameter type is
changed to `const version&` instead. this does not change
the semantic of the comparison operator. and is a more idiomatic
way to pass non-trivial struct as function parameters.
please note, because in C++20, both operator= and operator<=> are
symmetric, some of the operators in `multiprecision` are removed.
they are the symmetric form of the another variant. if they were
not removed, compiler would, for instance, find ambiguous
overloaded operator '=='.
this change is a cleanup to modernize the code base with C++20
features.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closes#13687
This class exists for one purpose only: to serve as glue code between
dht::ring_position and boost::icl::interval_map. The latter requires
that keys in its intervals are:
* default constructible
* copyable
* have standalone compare operations
For this reason we have to wrap `dht::ring_position` in a class,
together with a schema to provide all this. This is
`compatible_ring_position`. There is one further requirement by code
using the interval map: it wants to do lookups without copying the
lookup key(s). To solve this, we came up with
`compatible_ring_position_or_view` which is a union of a key or a key
view + schema. As we recently found out, boost::icl copies its keys **a
lot**. It seems to assume these keys are cheap to copy and carelessly
copies them around even when iterating over the map. But
`compatible_ring_position_or_view` is not cheap to copy as it copies a
`dht::ring_position` which allocates, and it does that via an
`std::optional` and `std::variant` to add insult to injury.
This patch make said class cheap to copy, by getting rid of the variant
and storing the `dht::ring_position` via a shared pointer. The view is
stored separately and either points to the ring position stored in the
shared pointer or to an outside ring position (for lookups).
Fixes: #11669Closes#11670
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.
