moved from utility

[SVN r21630]

example/transform_iterator_example.cpp

@@ -0,0 +1,78 @@
+// (C) Copyright Jeremy Siek 2000-2004. 
+// Permission to copy, use, modify, sell and distribute this software
+// is granted provided this copyright notice appears in all
+// copies. This software is provided "as is" without express or
+// implied warranty, and with no claim as to its suitability for any
+// purpose.
+
+
+#include <functional>
+#include <algorithm>
+#include <iostream>
+#include <boost/iterator/transform_iterator.hpp>
+
+// What a bummer. We can't use std::binder1st with transform iterator
+// because it does not have a default constructor. Here's a version
+// that does.
+
+namespace boost {
+
+  template <class Operation> 
+  class binder1st
+    : public std::unary_function<typename Operation::second_argument_type,
+                                 typename Operation::result_type> {
+  protected:
+    Operation op;
+    typename Operation::first_argument_type value;
+  public:
+    binder1st() { } // this had to be added!
+    binder1st(const Operation& x,
+              const typename Operation::first_argument_type& y)
+        : op(x), value(y) {}
+    typename Operation::result_type
+    operator()(const typename Operation::second_argument_type& x) const {
+      return op(value, x); 
+    }
+  };
+
+  template <class Operation, class T>
+  inline binder1st<Operation> bind1st(const Operation& op, const T& x) {
+    typedef typename Operation::first_argument_type arg1_type;
+    return binder1st<Operation>(op, arg1_type(x));
+  }
+
+} // namespace boost
+
+int
+main(int, char*[])
+{
+  // This is a simple example of using the transform_iterators class to
+  // generate iterators that multiply the value returned by dereferencing
+  // the iterator. In this case we are multiplying by 2.
+  // Would be cooler to use lambda library in this example.
+
+  int x[] = { 1, 2, 3, 4, 5, 6, 7, 8 };
+  const int N = sizeof(x)/sizeof(int);
+
+  typedef boost::binder1st< std::multiplies<int> > Function;
+  typedef boost::transform_iterator<Function, int*> doubling_iterator;
+
+  doubling_iterator i(x, boost::bind1st(std::multiplies<int>(), 2)),
+    i_end(x + N, boost::bind1st(std::multiplies<int>(), 2));
+
+  std::cout << "multiplying the array by 2:" << std::endl;
+  while (i != i_end)
+    std::cout << *i++ << " ";
+  std::cout << std::endl;
+
+  std::cout << "adding 4 to each element in the array:" << std::endl;
+
+  std::copy(boost::make_transform_iterator(x, boost::bind1st(std::plus<int>(), 4)),
+            boost::make_transform_iterator(x + N, boost::bind1st(std::plus<int>(), 4)),
+            std::ostream_iterator<int>(std::cout, " "));
+  std::cout << std::endl;
+  
+  return 0;
+}
+
+