1 // (C) Copyright Jeremy Siek 2000-2004.
2 // Distributed under the Boost Software License, Version 1.0. (See
3 // accompanying file LICENSE_1_0.txt or copy at
4 // http://www.boost.org/LICENSE_1_0.txt)
5
6
7 #include <functional>
8 #include <algorithm>
9 #include <iostream>
10 #include <boost/iterator/transform_iterator.hpp>
11
12 // What a bummer. We can't use std::binder1st with transform iterator
13 // because it does not have a default constructor. Here's a version
14 // that does.
15
16 namespace boost {
17
18 template <class Operation>
19 class binder1st {
20 public:
21 typedef typename Operation::result_type result_type;
22 typedef typename Operation::second_argument_type argument_type;
23 protected:
24 Operation op;
25 typename Operation::first_argument_type value;
26 public:
binder1st()27 binder1st() { } // this had to be added!
binder1st(const Operation & x,const typename Operation::first_argument_type & y)28 binder1st(const Operation& x,
29 const typename Operation::first_argument_type& y)
30 : op(x), value(y) {}
31 typename Operation::result_type
operator ()(const typename Operation::second_argument_type & x) const32 operator()(const typename Operation::second_argument_type& x) const {
33 return op(value, x);
34 }
35 };
36
37 template <class Operation, class T>
bind1st(const Operation & op,const T & x)38 inline binder1st<Operation> bind1st(const Operation& op, const T& x) {
39 typedef typename Operation::first_argument_type arg1_type;
40 return binder1st<Operation>(op, arg1_type(x));
41 }
42
43 } // namespace boost
44
45 int
main(int,char * [])46 main(int, char*[])
47 {
48 // This is a simple example of using the transform_iterators class to
49 // generate iterators that multiply the value returned by dereferencing
50 // the iterator. In this case we are multiplying by 2.
51 // Would be cooler to use lambda library in this example.
52
53 int x[] = { 1, 2, 3, 4, 5, 6, 7, 8 };
54 const int N = sizeof(x)/sizeof(int);
55
56 typedef boost::binder1st< std::multiplies<int> > Function;
57 typedef boost::transform_iterator<Function, int*> doubling_iterator;
58
59 doubling_iterator i(x, boost::bind1st(std::multiplies<int>(), 2)),
60 i_end(x + N, boost::bind1st(std::multiplies<int>(), 2));
61
62 std::cout << "multiplying the array by 2:" << std::endl;
63 while (i != i_end)
64 std::cout << *i++ << " ";
65 std::cout << std::endl;
66
67 std::cout << "adding 4 to each element in the array:" << std::endl;
68
69 std::copy(boost::make_transform_iterator(x, boost::bind1st(std::plus<int>(), 4)),
70 boost::make_transform_iterator(x + N, boost::bind1st(std::plus<int>(), 4)),
71 std::ostream_iterator<int>(std::cout, " "));
72 std::cout << std::endl;
73
74 return 0;
75 }
76