123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189190191192193194195196197198199200201202203204205206207208209210211212213214215216 |
- [section:transform Transform Iterator]
- The transform iterator adapts an iterator by modifying the
- `operator*` to apply a function object to the result of
- dereferencing the iterator and returning the result.
- [h2 Example]
- This is a simple example of using the transform_iterators class to
- generate iterators that multiply (or add to) the value returned by
- dereferencing the iterator. It 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;
- The output is:
- multiplying the array by 2:
- 2 4 6 8 10 12 14 16
- adding 4 to each element in the array:
- 5 6 7 8 9 10 11 12
- The source code for this example can be found
- [@../example/transform_iterator_example.cpp here].
- [h2 Reference]
- [h3 Synopsis]
- template <class UnaryFunction,
- class Iterator,
- class Reference = use_default,
- class Value = use_default>
- class transform_iterator
- {
- public:
- typedef /* see below */ value_type;
- typedef /* see below */ reference;
- typedef /* see below */ pointer;
- typedef iterator_traits<Iterator>::difference_type difference_type;
- typedef /* see below */ iterator_category;
- transform_iterator();
- transform_iterator(Iterator const& x, UnaryFunction f);
- template<class F2, class I2, class R2, class V2>
- transform_iterator(
- transform_iterator<F2, I2, R2, V2> const& t
- , typename enable_if_convertible<I2, Iterator>::type* = 0 // exposition only
- , typename enable_if_convertible<F2, UnaryFunction>::type* = 0 // exposition only
- );
- UnaryFunction functor() const;
- Iterator const& base() const;
- reference operator*() const;
- transform_iterator& operator++();
- transform_iterator& operator--();
- private:
- Iterator m_iterator; // exposition only
- UnaryFunction m_f; // exposition only
- };
- If `Reference` is `use_default` then the `reference` member of
- `transform_iterator` is[br]
- `result_of<const UnaryFunction(iterator_traits<Iterator>::reference)>::type`.
- Otherwise, `reference` is `Reference`.
- If `Value` is `use_default` then the `value_type` member is
- `remove_cv<remove_reference<reference> >::type`. Otherwise,
- `value_type` is `Value`.
- If `Iterator` models Readable Lvalue Iterator and if `Iterator`
- models Random Access Traversal Iterator, then `iterator_category` is
- convertible to `random_access_iterator_tag`. Otherwise, if
- `Iterator` models Bidirectional Traversal Iterator, then
- `iterator_category` is convertible to
- `bidirectional_iterator_tag`. Otherwise `iterator_category` is
- convertible to `forward_iterator_tag`. If `Iterator` does not
- model Readable Lvalue Iterator then `iterator_category` is
- convertible to `input_iterator_tag`.
- [h3 Requirements]
- The type `UnaryFunction` must be Assignable, Copy Constructible, and
- the expression `f(*i)` must be valid where `f` is a const object of
- type `UnaryFunction`, `i` is an object of type `Iterator`, and
- where the type of `f(*i)` must be
- `result_of<const UnaryFunction(iterator_traits<Iterator>::reference)>::type`.
- The argument `Iterator` shall model Readable Iterator.
- [h3 Concepts]
- The resulting `transform_iterator` models the most refined of the
- following that is also modeled by `Iterator`.
- * Writable Lvalue Iterator if `transform_iterator::reference` is a non-const reference.
- * Readable Lvalue Iterator if `transform_iterator::reference` is a const reference.
- * Readable Iterator otherwise.
- The `transform_iterator` models the most refined standard traversal
- concept that is modeled by the `Iterator` argument.
- If `transform_iterator` is a model of Readable Lvalue Iterator then
- it models the following original iterator concepts depending on what
- the `Iterator` argument models.
- [table Category
- [[If `Iterator` models][then `transform_iterator` models]]
- [[Single Pass Iterator][Input Iterator]]
- [[Forward Traversal Iterator][Forward Iterator]]
- [[Bidirectional Traversal Iterator][Bidirectional Iterator]]
- [[Random Access Traversal Iterator][Random Access Iterator]]
- ]
- If `transform_iterator` models Writable Lvalue Iterator then it is a
- mutable iterator (as defined in the old iterator requirements).
- `transform_iterator<F1, X, R1, V1>` is interoperable with
- `transform_iterator<F2, Y, R2, V2>` if and only if `X` is
- interoperable with `Y`.
- [h3 Operations]
- In addition to the operations required by the [link iterator.specialized.transform.concepts concepts] modeled by
- `transform_iterator`, `transform_iterator` provides the following
- operations:
- transform_iterator();
- [*Returns: ] An instance of `transform_iterator` with `m_f`
- and `m_iterator` default constructed.
- transform_iterator(Iterator const& x, UnaryFunction f);
- [*Returns: ] An instance of `transform_iterator` with `m_f`
- initialized to `f` and `m_iterator` initialized to `x`.
- template<class F2, class I2, class R2, class V2>
- transform_iterator(
- transform_iterator<F2, I2, R2, V2> const& t
- , typename enable_if_convertible<I2, Iterator>::type* = 0 // exposition only
- , typename enable_if_convertible<F2, UnaryFunction>::type* = 0 // exposition only
- );
- [*Returns: ] An instance of `transform_iterator` with `m_f`
- initialized to `t.functor()` and `m_iterator` initialized to
- `t.base()`.[br]
- [*Requires: ] `OtherIterator` is implicitly convertible to `Iterator`.
- UnaryFunction functor() const;
- [*Returns: ] `m_f`
- Iterator const& base() const;
- [*Returns: ] `m_iterator`
- reference operator*() const;
- [*Returns: ] `m_f(*m_iterator)`
- transform_iterator& operator++();
- [*Effects: ] `++m_iterator`[br]
- [*Returns: ] `*this`
- transform_iterator& operator--();
- [*Effects: ] `--m_iterator`[br]
- [*Returns: ] `*this`
- [endsect]
|