Re: Throwing default constructors of containers - a 2nd attempt for Rani Sharoni
[To the mods: This is not a self-reply, this is my answer to Rani
Sharoni]
I think that the application that you mentioned make sense but it can
be achieved even with having no-fail default constructor.
For allocation failures inside of default ctor the code can fallback
to zero capacity and avoid throwing.
Such approach make sense specifically for std::vector and std::string
for which zero capacity is not a special case.
Yes, you are totally right!
Seems strange that there is such oversight in the dinkumware
implementation.
I'm sure that there is some reason.
I don't want to affront anyone, but personally I think that
this is an oversight. I also looked into my very old Rogue Wave
library which I mentioned in my previous posting and it has the
same behaviour to possibly fail in the default c'tor due to an
unprotected allocation attempt.
I meant that the implementation can have "strict mode" for testing in
which it calls some MightThrow() function in operations that might
throw even if the actual implementation can't throw.
For example, std::list default ctor will contain call to MightThrow()
since according to the specification it might throw.
In this way the code can be strictly tested according to the
specifications and therefore the implementation can avoid potential
behavioral backward compatibility issues (i.e. breaking changes).
Ah, I see, you meant the basic principle of instrument code for
software fault injection! And no, I'm not aware of any standard
library,
which provides such facilities. The Dinkumware library uses checked
iterators and checked predicates depending on your built options,
but this is probably not comparable to a perturbation function.
I'm not sure how far-reaching your thoughts are but I would not
like a basic guarantee that *every* container must have a non-failable
default c'tor (You did not say that, I just want to make sure this
point).
I explicitly conditioned the non throwing default ctor for cases in
which it "make sense".
It probably make sense for vector, deque, string and list. Maybe for
map and probably not for hash-table.
I was thinking about filing a defect report if it's reasonable to do
so.
I applaud your effords - currently we have rather thin ice here,
IMO, which is probably related to the fact that the provision
of only some and only very basic failure guarantees had been
added as a last-minute action during the standardization process
in autumn/winter 1997 (as David already explained).
Greetings and a Good Night (in Germany...) wishes
Daniel
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