Re: Is boost::lexical_cast<>() always bijective?
On Mar 3, 7:25 am, Alex Vinokur <ale...@users.sourceforge.net> wrote:
Is boost::lexical_cast<>() always bijective?
In other words:
// --------------------------------------
template <class From, class To>
bool type_cast (const From& i_from, To& o_to)
{
bool ret = true;
try
{
o_to = boost::lexical_cast<To>(i_from);
}
catch(boost::bad_lexical_cast &)
{
ret = false;
}
return ret;
}
// --------------------------
T1 t1 = <some value>;
T2 t2;
if (type_cast (t1, t2))
{
assert (type_cast (t2, t1)); // does it always succeed?
}
Obviously not, since a user can define << and >> anyway he
pleases (or even define one, and not the other).
And that's not bijection. Bijection would guarantee a round
trip, with t1 equal to its initial value after the second
conversion, with all values in T1 having a mapping to a distinct
value in T2, and all values in T2 being the result of some
mapping from T1. Which, of course, is bound to fail as soon as
the types don't have the same number of values. Thus, string to
double may fail, and even when it succeeds, converting that
double back to string may result in a different value.
--
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