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>
A lightweight, trivially copyable and movable view for fragment ranges.
Allows for uniform treatment of all kinds of ranges, i.e. treating all
of them as a view. Currently `fragment_range.hh` provides lightweight,
view-like adaptors for empty and single-fragment ranges (`bytes_view`). To
allow code to treat owning multi-fragment ranges the shame way as the
former two, we need a view for the latter as well -- this is
`fragment_range_view`.
