id	summary	reporter	owner	description	type	status	milestone	component	version	severity	resolution	keywords	cc
2578	Add double-bounded version of outputting algorithms	Daryle Walker	Neil Groves	"(I thought there was an algorithms component.  But I don't see it, so I left the ""Component"" field as ""None."")

Many of the standard algorithms transfer data from one sequence to another, using iterators to define the bounds of said sequences.  Parameters for such sequences always include the beginning iterator.  But, frequently, only the first sequence has its ending iterator also passed; all the other sequences are assumed to be at least as long as the first one.  Confirming this is essential for robustness, and sometimes determining the length of a sequence relative to another in advance is non-trivial.  (It may involve manual counting through iterating over the whole sequence, which could be slow.  And it could be devastating if one of  the measured sequences is single-pass.)

The alternative is to make algorithms that take both the beginning and ending iterators for every sequence and automatically stop as soon as any of them end.  Obviously, this cannot work with output iterators, and such sequences need to work with forward (or above) iteration instead.  For instance, `std::copy` can go from:

{{{
template < typename InIter, typename OutIter >
OutIter  copy( InIter b, InIter e, OutIter o )
{ while ( b != e )  *o++ = *b++; return o; }
}}}

to:

{{{
template < typename InIter, typename ForIter >
pair<bool, ForIter>  copy_db( InIter sb, InIter se, ForIter db, ForIter de )  {
    while ( sb != se && db != de )
        *db++ = *sb++;
    return make_pair( sb == se, db );
}
}}}

The first sequence may be a single-pass input-iterator, so it can only return a Boolean flag if it reached its end.  The second sequence must be (at least) a forward-iterator, so a copy of the updated iterator can be returned.

Examples from the (C++ 2003) standard that could use such adaptations are: `equal`, `mismatch`, `copy`, `copy_backward`, `transform`, `swap_ranges`, `replace_copy`, `replace_copy_if`, `remove_copy`, `remove_copy_if`, `unique_copy`, `reverse_copy`, `rotate_copy`, `merge`, `set_union`, `set_intersection`, `set_difference`, `set_symmetric_difference`, `inner_product`, `partial_sum`, and `adjacent_difference`.  (Some return types may vary.)
"	Feature Requests	closed	Boost 1.38.0	range	Boost 1.37.0	Not Applicable	fixed	algorithm iterator bound