Re: [boost] Interest in StaticVector - fixed capacity vector

Subject: Re: [boost] Interest in StaticVector - fixed capacity vector
From: Peter Myerscough-Jackopson (peter.myerscough-jackopson_at_[hidden])
Date: 2011-10-11 04:48:23

>-----Original Message-----
>From: boost-bounces_at_[hidden]
[mailto:boost-bounces_at_[hidden]] On Behalf Of Marshall Clow
>Sent: 10 October 2011 23:36
>To: boost_at_[hidden]
>Subject: Re: [boost] Interest in StaticVector - fixed capacity vector
>
>On Oct 10, 2011, at 3:47 AM, Peter Myerscough-Jackopson wrote:
>
>> Andrew Hundt <athundt <at> gmail.com> writes:
>> 
>>> 
>>> On Sun, Aug 14, 2011 at 5:55 AM, Andrew Hundt <athundt <at>
gmail.com> wrote:
>>> 
>> <snip>
>>>>  three.push_back(2);  // size: 2 capacity: 3
>>>>  three.push_back(3);
>>>> 
>>>>  three.push_back(1); // throws std::out_of_range exception
indicating the
>>>> capacity has been exceeded
>> 
>> Is there any chance that the error behaviour code be configurable.
StaticVector
>> looks ideal for embedded environments, BUT commonly exceptions are
disabled in
>> such an environment. It would be nice to have asserts instead of
exceptions
>> available in all cases, so that a programmer can check for room on a
push_back 
>> prior to calling it. A specific StaticVector macro would suffice for
those that
>> need it. 
>
>IMHO, That's the whole point of using BOOST_THROW_EXCEPTION(x) instead
of a naked "throw x"
>
>If exceptions are disabled, then BOOST_THROW_EXCEPTION just calls
exit().
>

BOOST_THROW_EXCEPTION can be set to call a user defined function
boost_throw_exception, I am unaware of BOOST_THROW_EXCEPTION calling
exit(). The real issue is that even setting BOOST_NO_EXCEPTION and
BOOST_EXCEPTION_DISABLE, the user of a library is still required to
defined the boost_throw_exception function EVEN if the user checks that
calls are valid, i.e. the user performs their own capacitycheck and
rangecheck prior to calling. This means that you cannot compile up a
library including StaticVector without exceptions without defining
boost_throw_exception, even though because you check conditions prior to
calling functions. This pollutes the library unnecessarily, and means
users of a library that uses StaticVector have to provide a function
that is not used (boost_throw_exception) or that if they have defined it
for their own needs then it is somewhat concerning that an imported
library may appear to want to call it. Both of these are bad, and the
same issue exists inside boost::function. To resolve this it would be
useful to have an extension to the interface in some form to allow a
pushing and popping action to occur without a range/capacity check
function that can throw, but I would like to propose that an assert is
called instead. To maintain safety the checking functions could return
success/failure, and the calling functions maintain the object's state
invariants based upon the return code. 

Alternatively the push/pop functions could also return bool signifying
success/failure.

In looking at this I also note that there is a StaticVector( Iter begin,
Iter end ) that calls capacitycheck(). This then potentially throws, is
this truly desirable in a constructor? I see in a number of places where
the StaticVector is essentially copying from another unknown storage
class that could be larger than the StatcVector that it also could
throw, did you consider merely copying all that could be copied? i.e.
the first N objects are copied. I can't think if that would be better or
worse? It would certainly circumvent the need for checking/throwing in
some places.

Yours,

Peter

Ps. As an aside the capacity check function could be static.