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>
Each IMR type needs its own LSA migrator. It is possible that user will
provide a migrator for a different type than the one which instance is
being created. This patch adds compile-time detection of that bug.
IMR objects may own memory. object_allocator takes care of allocating
memory for all owned objects during the serialisation of their owner.
In practice a writer of the parent object would accept a helper object
created by object_allocator. That helper object would be either
responsible for computing the size of buffers that have to be allocated
or perform the actual serialisation in the same two phase manner as it
is done for the parent IMR object.
