Compile Time Tags

Iterators and circulators as well as different categories of circulators can be distinguished with the use of discriminating functions and the following circulator tags.

A couple of base classes simplify the task of writing own circulators. They declare the appropriate tags and the local types needed for circulators. To use the tags or base classes only it is sufficient to include:

See also

query_circulator_or_iterator

Circulator_traits

Assert_circulator

CGAL_For_all

is_empty_range

Circulator

Example

The above declarations can be used to distinguish between iterators and circulators and between different circulator categories. The assertions can be used to protect a templatized algorithm against instantiations that do not fulfill the requirements. The following example program illustrates both.

File Circulator/circulator_prog3.cpp

#include <cassert>
#include <list>
#include <CGAL/circulator.h>
 
template <class C> inline  int foo( C c, std::forward_iterator_tag) {
    CGAL::Assert_circulator( c);
    CGAL::Assert_forward_category( c);
    return 1;
}
template <class C> inline  int foo( C c, std::random_access_iterator_tag) {
    CGAL::Assert_circulator( c);
    CGAL::Assert_random_access_category( c);
    return 2;
}
template <class I> inline  int foo( I i, CGAL::Iterator_tag) {
    CGAL::Assert_iterator( i);
    return 3;
}
 
template <class C> inline  int foo( C c, CGAL::Circulator_tag) {
    CGAL::Assert_circulator( c);
    typedef std::iterator_traits<C> Traits;
    typedef typename Traits::iterator_category iterator_category;
    return foo( c, iterator_category());
}
template <class IC> inline  int foo( IC ic) {
    typedef CGAL::Circulator_traits<IC> Traits;
    typedef typename Traits::category category;
    return foo( ic, category());
}
 
int main() {
    typedef CGAL::Forward_circulator_base<int>       F;
    typedef CGAL::Random_access_circulator_base<int> R;
    F f = F();
    R r = R();
    std::list<int> l;
    assert( foo( f)         == 1);
    assert( foo( r)         == 2);
    assert( foo( l.begin()) == 3);
    return 0;
}

Classes
struct	CGAL::Circulator_tag
	A tag for any circulator type. More...
struct	CGAL::Iterator_tag
	A tag for any iterator type. More...
struct	CGAL::Forward_circulator_tag
struct	CGAL::Bidirectional_circulator_tag
struct	CGAL::Random_access_circulator_tag