[RFC] libstdc++/9626 and std::vector constructors

[Paolo Carlini]

Nathan Myers wrote:

>They are not equivalent, but the standard explicitly allows specified
>default-argument functions to be expanded into overloads.  Wherever
>practical, our library should do it.  We should do it as much as 
>possible now, because it risks breaking the ABI to do it later.
>Breaking up the interface very often creates optimization opportunities.
>Not breaking it up may foreclose those opportunities until the next time
>we choose to break the ABI.
>
>In the case of the vector constructor, *not* overloading would mean that 
>you construct an extra copy of the object, unnecessarily.
>
Ah! I suspected that could have to do with optimizations...

Anyway, many thanks Nathan! As often happens, I learned _very_ interesting
things from your reply.

Paolo.