Modifier_base<R> is an abstract base class providing the interface for any modifier. A modifier is a function object derived from Modifier_base<R> that implements the pure virtual member function operator(), which accepts a single reference parameter R& on which the modifier is allowed to work. R is the type of the internal representation that is to be modified.

#include <CGAL/Modifier_base.h>


typedef R Representation; the internal representation type.


virtual void modifier.operator() ( R& rep)
Postcondition: rep is a valid representation.


The following fragment defines a class A with an internal representation i of type int. It provides a member function delegate(), which gives a modifier access to the internal variable and checks validity thereafter. The example modifier sets the internal variable to 42. The example function applies the modifier to an instance of class A.

class A {
    int i;  // protected internal representation
    void delegate( CGAL::Modifier_base<int>& modifier) {
        CGAL_postcondition( i > 0);  // check validity

struct Modifier : public CGAL::Modifier_base<int> {
    void operator()( int& rep) { rep = 42;}

void use_it() {
    A a;
    Modifier m;
    a.delegate(m);  // a.i == 42 and A has checked that A::i > 0.