flow: Basic_blob et al should probably be non-copyable (but remain movable) via ctor/assignment (explicit copying OK).

[ygoldfeld]

flow::util::Basic_blob et al should probably be non-copyable (but remain movable) via ctor/assignment (explicit copying OK).

While measures are being taken elsewhere to avoid unnecessary stealth-copying in containers (due to lacking noexcept on Basic_blob/etc. move ctor and assignment), it raised the design question of whether it is even wise for Basic_blob et al to have copy ctor and copy assignment in the first place. (Having explicit method and possibly a static "ctor" factory to achieve copying can continue to be available. IIRC, there's assign() and such already.) The rationale is that, well, consider how Blob et al won't even allocate in the first place, unless one ensures the *this is zero() (null, no buffer owned) first. Why should it copy without the user absolutely explicitly asking for it? Probably it should not.

However it might be best to provide a copy ctor/assignment-enabled subclass for each such Basic_blob/etc. - as such a thing is conceivably still useful.

Note this would be a breaking change (but likely won't affect any extant production code).

Priority: low-medium. Nice feature but certainly are getting by without it.

[ygoldfeld]

Tactical note: Blob_with_log_context lacks assign(), because operator=(const B&) would do exactly the same (not the case for Basic_blob, due to assign() taking optional Logger* unlike the operator). If we eliminate operator=(), then perhaps assign() will need to be added.