1 // (C) Copyright David Abrahams 2002.
2 // (C) Copyright Jeremy Siek 2002.
3 // (C) Copyright Thomas Witt 2002.
4 // Distributed under the Boost Software License, Version 1.0. (See
5 // accompanying file LICENSE_1_0.txt or copy at
6 // http://www.boost.org/LICENSE_1_0.txt)
7 #ifndef BOOST_ITERATOR_FACADE_23022003THW_HPP
8 #define BOOST_ITERATOR_FACADE_23022003THW_HPP
10 #include <boost/iterator.hpp>
11 #include <boost/iterator/interoperable.hpp>
12 #include <boost/iterator/iterator_traits.hpp>
14 #include <boost/iterator/detail/facade_iterator_category.hpp>
15 #include <boost/iterator/detail/enable_if.hpp>
17 #include <boost/implicit_cast.hpp>
18 #include <boost/static_assert.hpp>
20 #include <boost/type_traits/is_same.hpp>
21 #include <boost/type_traits/add_const.hpp>
22 #include <boost/type_traits/add_pointer.hpp>
23 #include <boost/type_traits/remove_const.hpp>
24 #include <boost/type_traits/remove_reference.hpp>
25 #include <boost/type_traits/is_convertible.hpp>
26 #include <boost/type_traits/is_pod.hpp>
28 #include <boost/mpl/eval_if.hpp>
29 #include <boost/mpl/if.hpp>
30 #include <boost/mpl/or.hpp>
31 #include <boost/mpl/and.hpp>
32 #include <boost/mpl/not.hpp>
33 #include <boost/mpl/always.hpp>
34 #include <boost/mpl/apply.hpp>
35 #include <boost/mpl/identity.hpp>
37 #include <boost/iterator/detail/config_def.hpp> // this goes last
41 // This forward declaration is required for the friend declaration
42 // in iterator_core_access
43 template <class I, class V, class TC, class R, class D> class iterator_facade;
47 // A binary metafunction class that always returns bool. VC6
48 // ICEs on mpl::always<bool>, probably because of the default
52 template <class T, class U>
60 // enable if for use in operator implementation.
67 struct enable_if_interoperable
68 #if BOOST_WORKAROUND(BOOST_MSVC, <= 1300)
70 typedef typename mpl::if_<
72 is_convertible<Facade1, Facade2>
73 , is_convertible<Facade2, Facade1>
80 : ::boost::iterators::enable_if<
82 is_convertible<Facade1, Facade2>
83 , is_convertible<Facade2, Facade1>
91 // Generates associated types for an iterator_facade with the
96 , class CategoryOrTraversal
100 struct iterator_facade_types
102 typedef typename facade_iterator_category<
103 CategoryOrTraversal, ValueParam, Reference
104 >::type iterator_category;
106 typedef typename remove_const<ValueParam>::type value_type;
108 typedef typename mpl::eval_if<
109 detail::iterator_writability_disabled<ValueParam,Reference>
110 , add_pointer<const value_type>
111 , add_pointer<value_type>
114 # if defined(BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION) \
115 && (BOOST_WORKAROUND(_STLPORT_VERSION, BOOST_TESTED_AT(0x452)) \
116 || BOOST_WORKAROUND(BOOST_DINKUMWARE_STDLIB, BOOST_TESTED_AT(310))) \
117 || BOOST_WORKAROUND(BOOST_RWSTD_VER, BOOST_TESTED_AT(0x20101)) \
118 || BOOST_WORKAROUND(BOOST_DINKUMWARE_STDLIB, <= 310)
120 // To interoperate with some broken library/compiler
121 // combinations, user-defined iterators must be derived from
122 // std::iterator. It is possible to implement a standard
123 // library for broken compilers without this limitation.
124 # define BOOST_ITERATOR_FACADE_NEEDS_ITERATOR_BASE 1
127 iterator<iterator_category, value_type, Difference, pointer, Reference>
132 // iterators whose dereference operators reference the same value
133 // for all iterators into the same sequence (like many input
134 // iterators) need help with their postfix ++: the referenced
135 // value must be read and stored away before the increment occurs
136 // so that *a++ yields the originally referenced element and not
138 template <class Iterator>
139 class postfix_increment_proxy
141 typedef typename iterator_value<Iterator>::type value_type;
143 explicit postfix_increment_proxy(Iterator const& x)
147 // Returning a mutable reference allows nonsense like
148 // (*r++).mutate(), but it imposes fewer assumptions about the
149 // behavior of the value_type. In particular, recall taht
150 // (*r).mutate() is legal if operator* returns by value.
154 return this->stored_value;
157 mutable value_type stored_value;
161 // In general, we can't determine that such an iterator isn't
162 // writable -- we also need to store a copy of the old iterator so
163 // that it can be written into.
164 template <class Iterator>
165 class writable_postfix_increment_proxy
167 typedef typename iterator_value<Iterator>::type value_type;
169 explicit writable_postfix_increment_proxy(Iterator const& x)
174 // Dereferencing must return a proxy so that both *r++ = o and
175 // value_type(*r++) can work. In this case, *r is the same as
176 // *r++, and the conversion operator below is used to ensure
178 writable_postfix_increment_proxy const&
184 // Provides readability of *r++
185 operator value_type&() const
190 // Provides writability of *r++
192 T const& operator=(T const& x) const
194 *this->stored_iterator = x;
198 // This overload just in case only non-const objects are writable
200 T& operator=(T& x) const
202 *this->stored_iterator = x;
207 operator Iterator const&() const
209 return stored_iterator;
213 mutable value_type stored_value;
214 Iterator stored_iterator;
217 # ifdef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
219 template <class Reference, class Value>
220 struct is_non_proxy_reference_impl
225 static typename mpl::if_<
228 , Value const volatile*
232 >::type& helper(R const&);
234 BOOST_STATIC_CONSTANT(bool, value = sizeof(helper(r)) == 1);
237 template <class Reference, class Value>
238 struct is_non_proxy_reference
240 is_non_proxy_reference_impl<Reference, Value>::value
244 template <class Reference, class Value>
245 struct is_non_proxy_reference
247 typename remove_reference<Reference>::type
249 , Value const volatile*
254 // A metafunction to choose the result type of postfix ++
256 // Because the C++98 input iterator requirements say that *r++ has
257 // type T (value_type), implementations of some standard
258 // algorithms like lexicographical_compare may use constructions
263 // If *r++ returns a proxy (as required if r is writable but not
264 // multipass), this sort of expression will fail unless the proxy
265 // supports the operator<. Since there are any number of such
266 // operations, we're not going to try to support them. Therefore,
267 // even if r++ returns a proxy, *r++ will only return a proxy if
268 // *r also returns a proxy.
269 template <class Iterator, class Value, class Reference, class CategoryOrTraversal>
270 struct postfix_increment_result
273 // A proxy is only needed for readable iterators
274 is_convertible<Reference,Value const&>
276 // No multipass iterator can have values that disappear
277 // before positions can be re-visited
280 typename iterator_category_to_traversal<CategoryOrTraversal>::type
281 , forward_traversal_tag
286 is_non_proxy_reference<Reference,Value>
287 , postfix_increment_proxy<Iterator>
288 , writable_postfix_increment_proxy<Iterator>
290 , mpl::identity<Iterator>
294 // operator->() needs special support for input iterators to strictly meet the
295 // standard's requirements. If *i is not a reference type, we must still
296 // produce a lvalue to which a pointer can be formed. We do that by
297 // returning an instantiation of this special proxy class template.
299 struct operator_arrow_proxy
301 operator_arrow_proxy(T const* px) : m_value(*px) {}
302 T* operator->() const { return &m_value; }
303 // This function is needed for MWCW and BCC, which won't call operator->
304 // again automatically per 13.3.1.2 para 8
305 operator T*() const { return &m_value; }
309 // A metafunction that gets the result type for operator->. Also
310 // has a static function make() which builds the result from a
312 template <class ValueType, class Reference, class Pointer>
313 struct operator_arrow_result
315 // CWPro8.3 won't accept "operator_arrow_result::type", and we
316 // need that type below, so metafunction forwarding would be a
317 // losing proposition here.
318 typedef typename mpl::if_<
319 is_reference<Reference>
321 , operator_arrow_proxy<ValueType>
324 static type make(Reference x)
326 return implicit_cast<type>(&x);
330 # if BOOST_WORKAROUND(BOOST_MSVC, < 1300)
333 struct operator_arrow_result<int, int, int>
339 // A proxy return type for operator[], needed to deal with
340 // iterators that may invalidate referents upon destruction.
341 // Consider the temporary iterator in *(a + n)
342 template <class Iterator>
343 class operator_brackets_proxy
345 // Iterator is actually an iterator_facade, so we do not have to
346 // go through iterator_traits to access the traits.
347 typedef typename Iterator::reference reference;
348 typedef typename Iterator::value_type value_type;
351 operator_brackets_proxy(Iterator const& iter)
355 operator reference() const
360 operator_brackets_proxy& operator=(value_type const& val)
370 // A metafunction that determines whether operator[] must return a
371 // proxy, or whether it can simply return a copy of the value_type.
372 template <class ValueType, class Reference>
373 struct use_operator_brackets_proxy
376 // Really we want an is_copy_constructible trait here,
377 // but is_POD will have to suffice in the meantime.
378 boost::is_POD<ValueType>
379 , iterator_writability_disabled<ValueType,Reference>
384 template <class Iterator, class Value, class Reference>
385 struct operator_brackets_result
387 typedef typename mpl::if_<
388 use_operator_brackets_proxy<Value,Reference>
389 , operator_brackets_proxy<Iterator>
394 template <class Iterator>
395 operator_brackets_proxy<Iterator> make_operator_brackets_result(Iterator const& iter, mpl::true_)
397 return operator_brackets_proxy<Iterator>(iter);
400 template <class Iterator>
401 typename Iterator::value_type make_operator_brackets_result(Iterator const& iter, mpl::false_)
406 struct choose_difference_type
408 template <class I1, class I2>
411 # ifdef BOOST_NO_ONE_WAY_ITERATOR_INTEROP
412 iterator_difference<I1>
413 # elif BOOST_WORKAROUND(BOOST_MSVC, < 1300)
415 is_convertible<I2,I1>
416 , typename I1::difference_type
417 , typename I2::difference_type
421 is_convertible<I2,I1>
422 , iterator_difference<I1>
423 , iterator_difference<I2>
429 } // namespace detail
432 // Macros which describe the declarations of binary operators
433 # ifdef BOOST_NO_STRICT_ITERATOR_INTEROPERABILITY
434 # define BOOST_ITERATOR_FACADE_INTEROP_HEAD(prefix, op, result_type) \
436 class Derived1, class V1, class TC1, class R1, class D1 \
437 , class Derived2, class V2, class TC2, class R2, class D2 \
439 prefix typename mpl::apply2<result_type,Derived1,Derived2>::type \
441 iterator_facade<Derived1, V1, TC1, R1, D1> const& lhs \
442 , iterator_facade<Derived2, V2, TC2, R2, D2> const& rhs)
444 # define BOOST_ITERATOR_FACADE_INTEROP_HEAD(prefix, op, result_type) \
446 class Derived1, class V1, class TC1, class R1, class D1 \
447 , class Derived2, class V2, class TC2, class R2, class D2 \
449 prefix typename detail::enable_if_interoperable< \
451 , typename mpl::apply2<result_type,Derived1,Derived2>::type \
454 iterator_facade<Derived1, V1, TC1, R1, D1> const& lhs \
455 , iterator_facade<Derived2, V2, TC2, R2, D2> const& rhs)
458 # define BOOST_ITERATOR_FACADE_PLUS_HEAD(prefix,args) \
459 template <class Derived, class V, class TC, class R, class D> \
460 prefix Derived operator+ args
463 // Helper class for granting access to the iterator core interface.
465 // The simple core interface is used by iterator_facade. The core
466 // interface of a user/library defined iterator type should not be made public
467 // so that it does not clutter the public interface. Instead iterator_core_access
468 // should be made friend so that iterator_facade can access the core
469 // interface through iterator_core_access.
471 class iterator_core_access
473 # if defined(BOOST_NO_MEMBER_TEMPLATE_FRIENDS) \
474 || BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x551))
475 // Tasteless as this may seem, making all members public allows member templates
476 // to work in the absence of member template friends.
480 template <class I, class V, class TC, class R, class D> friend class iterator_facade;
482 # define BOOST_ITERATOR_FACADE_RELATION(op) \
483 BOOST_ITERATOR_FACADE_INTEROP_HEAD(friend,op, detail::always_bool2);
485 BOOST_ITERATOR_FACADE_RELATION(==)
486 BOOST_ITERATOR_FACADE_RELATION(!=)
488 BOOST_ITERATOR_FACADE_RELATION(<)
489 BOOST_ITERATOR_FACADE_RELATION(>)
490 BOOST_ITERATOR_FACADE_RELATION(<=)
491 BOOST_ITERATOR_FACADE_RELATION(>=)
492 # undef BOOST_ITERATOR_FACADE_RELATION
494 BOOST_ITERATOR_FACADE_INTEROP_HEAD(
495 friend, -, detail::choose_difference_type)
498 BOOST_ITERATOR_FACADE_PLUS_HEAD(
500 , (iterator_facade<Derived, V, TC, R, D> const&
501 , typename Derived::difference_type)
505 BOOST_ITERATOR_FACADE_PLUS_HEAD(
507 , (typename Derived::difference_type
508 , iterator_facade<Derived, V, TC, R, D> const&)
514 template <class Facade>
515 static typename Facade::reference dereference(Facade const& f)
517 return f.dereference();
520 template <class Facade>
521 static void increment(Facade& f)
526 template <class Facade>
527 static void decrement(Facade& f)
532 template <class Facade1, class Facade2>
533 static bool equal(Facade1 const& f1, Facade2 const& f2, mpl::true_)
538 template <class Facade1, class Facade2>
539 static bool equal(Facade1 const& f1, Facade2 const& f2, mpl::false_)
544 template <class Facade>
545 static void advance(Facade& f, typename Facade::difference_type n)
550 template <class Facade1, class Facade2>
551 static typename Facade1::difference_type distance_from(
552 Facade1 const& f1, Facade2 const& f2, mpl::true_)
554 return -f1.distance_to(f2);
557 template <class Facade1, class Facade2>
558 static typename Facade2::difference_type distance_from(
559 Facade1 const& f1, Facade2 const& f2, mpl::false_)
561 return f2.distance_to(f1);
565 // Curiously Recurring Template interface.
567 template <class I, class V, class TC, class R, class D>
568 static I& derived(iterator_facade<I,V,TC,R,D>& facade)
570 return *static_cast<I*>(&facade);
573 template <class I, class V, class TC, class R, class D>
574 static I const& derived(iterator_facade<I,V,TC,R,D> const& facade)
576 return *static_cast<I const*>(&facade);
580 // objects of this class are useless
581 iterator_core_access(); //undefined
585 // iterator_facade - use as a public base class for defining new
586 // standard-conforming iterators.
589 class Derived // The derived iterator type being constructed
591 , class CategoryOrTraversal
592 , class Reference = Value&
593 , class Difference = std::ptrdiff_t
595 class iterator_facade
596 # ifdef BOOST_ITERATOR_FACADE_NEEDS_ITERATOR_BASE
597 : public detail::iterator_facade_types<
598 Value, CategoryOrTraversal, Reference, Difference
600 # undef BOOST_ITERATOR_FACADE_NEEDS_ITERATOR_BASE
605 // Curiously Recurring Template interface.
609 return *static_cast<Derived*>(this);
612 Derived const& derived() const
614 return *static_cast<Derived const*>(this);
617 typedef detail::iterator_facade_types<
618 Value, CategoryOrTraversal, Reference, Difference
622 // For use by derived classes
623 typedef iterator_facade<Derived,Value,CategoryOrTraversal,Reference,Difference> iterator_facade_;
627 typedef typename associated_types::value_type value_type;
628 typedef Reference reference;
629 typedef Difference difference_type;
630 typedef typename associated_types::pointer pointer;
631 typedef typename associated_types::iterator_category iterator_category;
633 reference operator*() const
635 return iterator_core_access::dereference(this->derived());
638 typename detail::operator_arrow_result<
645 return detail::operator_arrow_result<
649 >::make(*this->derived());
652 typename detail::operator_brackets_result<Derived,Value,reference>::type
653 operator[](difference_type n) const
655 typedef detail::use_operator_brackets_proxy<Value,Reference> use_proxy;
657 return detail::make_operator_brackets_result<Derived>(
663 Derived& operator++()
665 iterator_core_access::increment(this->derived());
666 return this->derived();
669 # if BOOST_WORKAROUND(BOOST_MSVC, < 1300)
670 typename detail::postfix_increment_result<Derived,Value,Reference,CategoryOrTraversal>::type
673 typename detail::postfix_increment_result<Derived,Value,Reference,CategoryOrTraversal>::type
674 tmp(this->derived());
680 Derived& operator--()
682 iterator_core_access::decrement(this->derived());
683 return this->derived();
686 Derived operator--(int)
688 Derived tmp(this->derived());
693 Derived& operator+=(difference_type n)
695 iterator_core_access::advance(this->derived(), n);
696 return this->derived();
699 Derived& operator-=(difference_type n)
701 iterator_core_access::advance(this->derived(), -n);
702 return this->derived();
705 Derived operator-(difference_type x) const
707 Derived result(this->derived());
711 # if BOOST_WORKAROUND(BOOST_MSVC, < 1300)
712 // There appears to be a bug which trashes the data of classes
713 // derived from iterator_facade when they are assigned unless we
714 // define this assignment operator. This bug is only revealed
715 // (so far) in STLPort debug mode, but it's clearly a codegen
716 // problem so we apply the workaround for all MSVC6.
717 iterator_facade& operator=(iterator_facade const&)
724 # if !BOOST_WORKAROUND(BOOST_MSVC, < 1300)
725 template <class I, class V, class TC, class R, class D>
726 inline typename detail::postfix_increment_result<I,V,R,TC>::type
728 iterator_facade<I,V,TC,R,D>& i
732 typename detail::postfix_increment_result<I,V,R,TC>::type
733 tmp(*static_cast<I*>(&i));
743 // Comparison operator implementation. The library supplied operators
744 // enables the user to provide fully interoperable constant/mutable
745 // iterator types. I.e. the library provides all operators
746 // for all mutable/constant iterator combinations.
748 // Note though that this kind of interoperability for constant/mutable
749 // iterators is not required by the standard for container iterators.
750 // All the standard asks for is a conversion mutable -> constant.
751 // Most standard library implementations nowadays provide fully interoperable
752 // iterator implementations, but there are still heavily used implementations
753 // that do not provide them. (Actually it's even worse, they do not provide
754 // them for only a few iterators.)
756 // ?? Maybe a BOOST_ITERATOR_NO_FULL_INTEROPERABILITY macro should
757 // enable the user to turn off mixed type operators
759 // The library takes care to provide only the right operator overloads.
762 // bool operator==(Iterator, Iterator);
763 // bool operator==(ConstIterator, Iterator);
764 // bool operator==(Iterator, ConstIterator);
765 // bool operator==(ConstIterator, ConstIterator);
769 // In order to do so it uses c++ idioms that are not yet widely supported
770 // by current compiler releases. The library is designed to degrade gracefully
771 // in the face of compiler deficiencies. In general compiler
772 // deficiencies result in less strict error checking and more obscure
773 // error messages, functionality is not affected.
775 // For full operation compiler support for "Substitution Failure Is Not An Error"
776 // (aka. enable_if) and boost::is_convertible is required.
778 // The following problems occur if support is lacking.
783 // AdaptorA<Iterator1> a1;
784 // AdaptorA<Iterator2> a2;
786 // // This will result in a no such overload error in full operation
787 // // If enable_if or is_convertible is not supported
788 // // The instantiation will fail with an error hopefully indicating that
789 // // there is no operator== for Iterator1, Iterator2
790 // // The same will happen if no enable_if is used to remove
791 // // false overloads from the templated conversion constructor
797 // AdaptorA<Iterator> a;
798 // AdaptorB<Iterator> b;
800 // // This will result in a no such overload error in full operation
801 // // If enable_if is not supported the static assert used
802 // // in the operator implementation will fail.
803 // // This will accidently work if is_convertible is not supported.
809 # ifdef BOOST_NO_ONE_WAY_ITERATOR_INTEROP
810 # define BOOST_ITERATOR_CONVERTIBLE(a,b) mpl::true_()
812 # define BOOST_ITERATOR_CONVERTIBLE(a,b) is_convertible<a,b>()
815 # define BOOST_ITERATOR_FACADE_INTEROP(op, result_type, return_prefix, base_op) \
816 BOOST_ITERATOR_FACADE_INTEROP_HEAD(inline, op, result_type) \
818 /* For those compilers that do not support enable_if */ \
819 BOOST_STATIC_ASSERT(( \
820 is_interoperable< Derived1, Derived2 >::value \
822 return_prefix iterator_core_access::base_op( \
823 *static_cast<Derived1 const*>(&lhs) \
824 , *static_cast<Derived2 const*>(&rhs) \
825 , BOOST_ITERATOR_CONVERTIBLE(Derived2,Derived1) \
829 # define BOOST_ITERATOR_FACADE_RELATION(op, return_prefix, base_op) \
830 BOOST_ITERATOR_FACADE_INTEROP( \
832 , detail::always_bool2 \
837 BOOST_ITERATOR_FACADE_RELATION(==, return, equal)
838 BOOST_ITERATOR_FACADE_RELATION(!=, return !, equal)
840 BOOST_ITERATOR_FACADE_RELATION(<, return 0 >, distance_from)
841 BOOST_ITERATOR_FACADE_RELATION(>, return 0 <, distance_from)
842 BOOST_ITERATOR_FACADE_RELATION(<=, return 0 >=, distance_from)
843 BOOST_ITERATOR_FACADE_RELATION(>=, return 0 <=, distance_from)
844 # undef BOOST_ITERATOR_FACADE_RELATION
846 // operator- requires an additional part in the static assertion
847 BOOST_ITERATOR_FACADE_INTEROP(
849 , detail::choose_difference_type
853 # undef BOOST_ITERATOR_FACADE_INTEROP
854 # undef BOOST_ITERATOR_FACADE_INTEROP_HEAD
856 # define BOOST_ITERATOR_FACADE_PLUS(args) \
857 BOOST_ITERATOR_FACADE_PLUS_HEAD(inline, args) \
859 Derived tmp(static_cast<Derived const&>(i)); \
863 BOOST_ITERATOR_FACADE_PLUS((
864 iterator_facade<Derived, V, TC, R, D> const& i
865 , typename Derived::difference_type n
868 BOOST_ITERATOR_FACADE_PLUS((
869 typename Derived::difference_type n
870 , iterator_facade<Derived, V, TC, R, D> const& i
872 # undef BOOST_ITERATOR_FACADE_PLUS
873 # undef BOOST_ITERATOR_FACADE_PLUS_HEAD
877 #include <boost/iterator/detail/config_undef.hpp>
879 #endif // BOOST_ITERATOR_FACADE_23022003THW_HPP