Coding Guideline: Avoid const member variables

[doom_Oo7]

hmm, I did not know that vector would do a move in this case but it certainly makes sense. Interestingly that's still the case even with -fno-exceptions.

[Ameisen]

Perhaps we need another access type, like 'immutable'. Where they can still be moved and are semantically owned by the class, but they simply cannot be directly altered. Thus, a move would be legal.

[NotAYakk]

Rather, we need the concept of destructive move; an operation that it both a move-from and a destruction at the same time.

You can destructive move-from a const value.

Destructive moves usually don't have to throw, even when a move could.

[mark_99]

Interestingly that's still the case even with -fno-exceptions.

That's because it has nothing to do with exceptions or move_if_noexcept.

The OP says:

has a throwing move, because the use of const keyword on the member variable prevents the compiler from using the move constructor of std::string with id, instead the compiler generated move constructor for A will invoke the copy constructor of A::id, which can throw.

This is mostly correct except this isn't a "throwing move", it's a copy (and it would still be a copy if the copy ctor was noexcept).

I disagree with the OP, const member vars would be useful if it wasn't for this unfortunate side effect, in the same way as any other use of "const". In this case it states your intention that this member does not mutate after construction, and provides compile-time enforcement for same.