Version 5.0 The LEDA User Manual

We would have to write something like this:
while(it.valid()) {
if (G[it.get_node()]==red) do_something(it);
++it;
}
With the filter wrapper class we can add the test if the node is red to the behaviour of
the iterator.
struct RedPred {
bool operator() (const NodeIt& it) const {
return G[it.get_node()]==red; }
} redpred;
FilterNodeIt red_it(redpred,it);
This simplifies the loop to the following:
while(red_it.valid()) {
do_something(red_it);
++red_it; }
All ingredients of the comparison are hard-wired in struct RedPred: the type of the compared
values (color), the comparison value (red) and the binary comparison (equality).
The following class CompPred renders these three choices flexible.
13.10 Comparison Predicate ( CompPred )
1. Definition
An instance cp of class CompPred is a predicate comparator that produces
boolean values with the given compare function and the attribute associated with
an iterator.
#include < LEDA/graph/graph iterator.h >