Seastar recently lost support for the experimental Concepts Technical
Specification (TS) and gained support for C++20 concepts. Re-enable
concepts in Scylla by updating our use of concepts to the C++20
standard.
This change:
- peels off uses of the GCC6_CONCEPT macro
- removes inclusions of <seastar/gcc6-concepts.hh>
- replaces function-style concepts (no longer supported) with
equation-style concepts
- semicolons added and removed as needed
- deprecated std::is_pod replaced by recommended replacement
- updates return type constraints to use concepts instead of
type names (either std::same_as or std::convertible_to, with
std::same_as chosen when possible)
No attempt is made to improve the concepts; this is a specification
update only.
Message-Id: <20200531110254.2555854-1-avi@scylladb.com>
3ec889816 changed cell::make_collection() to take different code paths
depending whether its `data` argument is nothrow copyable/movable or
not. In case it is not, it is wrapped in a view to make it so (see the
above mentioned commit for a full explanation), relying on the methods
pre-existing requirement for callers to keep `data` alive while the
created writer is in use.
On closer look however it turns out that this requirement is neither
respected, nor enforced, at least not on the code level. The real
requirement is that the underlying data represented by `data` is kept
alive. If `data` is a view, it is not expected to be kept alive and
callers don't, it is instead copied into `make_collection()`.
Non-views however *are* expected to be kept alive. This makes the API
error prone.
To avoid any future errors due to this ambiguity, require all `data`
arguments to be nothrow copyable and movable. Callers are now required
to pass views of nonconforming objects.
This patch is a usability improvement and is not fixing a bug. The
current code works as-is because it happens to conform to the underlying
requirements.
Refs: #5575
Refs: #5341
Tests: unit(dev)
Signed-off-by: Botond Dénes <bdenes@scylladb.com>
Message-Id: <20200115084520.206947-1-bdenes@scylladb.com>
Use `utils::linearizing_input_stream` for the deserizalization of the
collection. Allows for avoiding the linearization of the entire cell
value, instead only linearizing individual values as they are
deserialized from the buffer.
`collection_type_impl::serialize_mutation_form`
became `collection_mutation(_view)_description::serialize`.
Previously callers had to cast their data_type down to collection_type
to use serialize_mutation_form. Now it's done inside `serialize`.
In the future `serialize` will be generalized to handle UDTs.
`collection_type_impl::deserialize_mutation_form`
became a free standing function `deserialize_collection_mutation`
with similiar benefits. Actually, noone needs to call this function
manually because of the next paragraph.
A common pattern consisting of linearizing data inside a `collection_mutation_view`
followed by calling `deserialize_mutation_form` has been abstracted out
as a `with_deserialized` method inside collection_mutation_view.
serialize_mutation_form_only_live was removed,
because it hadn't been used anywhere.
collection_type_impl::mutation became collection_mutation_description.
collection_type_impl::mutation_view became collection_mutation_view_description.
These classes now reside inside collection_mutation.hh.
Additional documentation has been written for these classes.
Related function implementations were moved to collection_mutation.cc.
This makes it easier to generalize these classes to non-frozen UDTs in future commits.
The new names (together with documentation) better describe their purpose.
The classes 'collection_mutation' and 'collection_mutation_view'
were moved to a separate header, collection_mutation.hh.
Implementations of functions that operate on these classes,
including some methods of collection_type_impl, were moved
to a separate compilation unit, collection_mutation.cc.
This makes it easier to modify these structures in future commits
in order to generalize them for non-frozen User Defined Types.
Some additional documentation has been written for collection_mutation.
