Re: How to write previous element in STL list
On Jul 28, 4:32 pm, Juha Nieminen <nos...@thanks.invalid> wrote:
Pascal J. Bourguignon wrote:
I don't know if the C++ standard does the same about operators such as
+, but indeed it might be expect that + is a O(1) operation.
You can write your own operator+ for your list iterators if
you want. There's nothing stopping you. (Except that I think
you can't template operator overloads, which is a bit of a
bummer, but you can overload the operator for specific list
types.)
Operator overloads can be template functions; there's no problem
there. The problem for operator+ on an std::list::iterator is
that if you try to write:
template< typename T >
typename std::list< T >::iterator
operator+(
typename std::list< T >::iterator
lhs,
int rhs )
{
std::advance( lhs, rhs ) ;
return lhs ;
}
, T is in a non-deduced context, which means that template
argument deduction fails, and no instantiation of the template
is added to the overload set. (You can, of course, still call
it with "::operator+<int>( i, 3 )", but that sort of defeats the
purpose of operator overloading.) And if you just write:
template< typename T >
T
operator+(
T lhs,
int rhs )
{
std::advance( lhs, rhs ) ;
return lhs ;
}
, you're going to match a lot of things you don't want it to
match, and probably cause problems elsewhere (ambiguous
overloads, or it might even be a better match than the intended
operator).
--
James Kanze (GABI Software) email:james.kanze@gmail.com
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