on 31.03.2010 at 20:15 Scott McMurray wrote :
I have a sketch of a way to offer both here: http://lists.boost.org/Archives/boost/2010/03/164346.php
i thought a while and came to a conclusion that making different flavors of xint as distinct types or different specializations or even policy based implementation is a good idea indeed particularly having xint::raw_integer and xint::integer (exception blocking and NaN are here) makes sense these two (possibly) implicitly share the value for run time efficiency (for fast convertions of one to another) then if 'op(xint::raw_integer)' wraps 'op(xint::integer)' the former checks for NaN and throws (otherwise 'op(xint::integer)' throws itself) if 'op(xint::integer)' wraps 'op(xint::raw_integer)' then the former catches the possible exception and returns NaN if exceptions are blocked but this case seems less efficient actually there are some things to think of
A "half-signaling" NaN (quietly manufactured but noisy when touched) seems to me a near-useless middle ground. This is a good point. When the option of a policy-based scheme for exception control was brought up I just sort of assumed on principle that it would somehow be useful. Can anyone give an example where a middle ground would be best?
i vote for quiet NaN since operations are throwing already by default but actually the original design was sane too for example xint::integer i; while ((i = foo())==NaN) //doing some important work ask_user_what_to_do(); //failed! worth it to try again? i think this is conscious was NaN a signaling one this would not be possible but if i try accidentally to use a NaN in an operation it throws like in the following example xint::integer i = bar(a); //fails sometimes because of its nature //if (i==NaN) do_something(); //oh! forgot to check if bar() i *= 2; //succeeded! here to indicate that 'bar()' may fail not as an exceptional situation but due to its nature we say that it returns NaN was NaN a signaling beast 'bar()' would throw anyway -- exception missuse -- Pavel P.S. if you notice a grammar mistake or weird phrasing in my message please point it out