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/static_assert.hpp>
12 #include <boost/iterator.hpp>
13 #include <boost/iterator/interoperable.hpp>
14 #include <boost/iterator/iterator_traits.hpp>
16 #include <boost/iterator/detail/facade_iterator_category.hpp>
17 #include <boost/iterator/detail/enable_if.hpp>
19 #include <boost/type_traits/is_same.hpp>
20 #include <boost/type_traits/add_const.hpp>
21 #include <boost/type_traits/add_pointer.hpp>
22 #include <boost/type_traits/remove_const.hpp>
23 #include <boost/type_traits/remove_reference.hpp>
24 #include <boost/type_traits/is_convertible.hpp>
25 #include <boost/type_traits/is_pod.hpp>
27 #include <boost/mpl/eval_if.hpp>
28 #include <boost/mpl/if.hpp>
29 #include <boost/mpl/or.hpp>
30 #include <boost/mpl/and.hpp>
31 #include <boost/mpl/not.hpp>
32 #include <boost/mpl/always.hpp>
33 #include <boost/mpl/apply.hpp>
34 #include <boost/mpl/identity.hpp>
36 #include <boost/iterator/detail/config_def.hpp> // this goes last
40 // This forward declaration is required for the friend declaration
41 // in iterator_core_access
42 template <class I, class V, class TC, class R, class D> class iterator_facade;
46 // A binary metafunction class that always returns bool. VC6
47 // ICEs on mpl::always<bool>, probably because of the default
51 template <class T, class U>
59 // enable if for use in operator implementation.
66 struct enable_if_interoperable
67 #if BOOST_WORKAROUND(BOOST_MSVC, <= 1300)
69 typedef typename mpl::if_<
71 is_convertible<Facade1, Facade2>
72 , is_convertible<Facade2, Facade1>
79 : ::boost::iterators::enable_if<
81 is_convertible<Facade1, Facade2>
82 , is_convertible<Facade2, Facade1>
90 // Generates associated types for an iterator_facade with the
95 , class CategoryOrTraversal
99 struct iterator_facade_types
101 typedef typename facade_iterator_category<
102 CategoryOrTraversal, ValueParam, Reference
103 >::type iterator_category;
105 typedef typename remove_const<ValueParam>::type value_type;
107 typedef typename mpl::eval_if<
108 detail::iterator_writability_disabled<ValueParam,Reference>
109 , add_pointer<typename add_const<value_type>::type>
110 , add_pointer<value_type>
113 # if defined(BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION) \
114 && (BOOST_WORKAROUND(_STLPORT_VERSION, BOOST_TESTED_AT(0x452)) \
115 || BOOST_WORKAROUND(BOOST_DINKUMWARE_STDLIB, BOOST_TESTED_AT(310))) \
116 || BOOST_WORKAROUND(BOOST_RWSTD_VER, BOOST_TESTED_AT(0x20101)) \
117 || BOOST_WORKAROUND(BOOST_DINKUMWARE_STDLIB, <= 310)
119 // To interoperate with some broken library/compiler
120 // combinations, user-defined iterators must be derived from
121 // std::iterator. It is possible to implement a standard
122 // library for broken compilers without this limitation.
123 # define BOOST_ITERATOR_FACADE_NEEDS_ITERATOR_BASE 1
126 iterator<iterator_category, value_type, Difference, pointer, Reference>
131 // iterators whose dereference operators reference the same value
132 // for all iterators into the same sequence (like many input
133 // iterators) need help with their postfix ++: the referenced
134 // value must be read and stored away before the increment occurs
135 // so that *a++ yields the originally referenced element and not
137 template <class Iterator>
138 class postfix_increment_proxy
140 typedef typename iterator_value<Iterator>::type value_type;
142 explicit postfix_increment_proxy(Iterator const& x)
146 // Returning a mutable reference allows nonsense like
147 // (*r++).mutate(), but it imposes fewer assumptions about the
148 // behavior of the value_type. In particular, recall taht
149 // (*r).mutate() is legal if operator* returns by value.
153 return this->stored_value;
156 mutable value_type stored_value;
160 // In general, we can't determine that such an iterator isn't
161 // writable -- we also need to store a copy of the old iterator so
162 // that it can be written into.
163 template <class Iterator>
164 class writable_postfix_increment_proxy
166 typedef typename iterator_value<Iterator>::type value_type;
168 explicit writable_postfix_increment_proxy(Iterator const& x)
173 // Dereferencing must return a proxy so that both *r++ = o and
174 // value_type(*r++) can work. In this case, *r is the same as
175 // *r++, and the conversion operator below is used to ensure
177 writable_postfix_increment_proxy const&
183 // Provides readability of *r++
184 operator value_type&() const
189 // Provides writability of *r++
191 T const& operator=(T const& x) const
193 *this->stored_iterator = x;
197 // This overload just in case only non-const objects are writable
199 T& operator=(T& x) const
201 *this->stored_iterator = x;
206 operator Iterator const&() const
208 return stored_iterator;
212 mutable value_type stored_value;
213 Iterator stored_iterator;
216 # ifdef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
218 template <class Reference, class Value>
219 struct is_non_proxy_reference_impl
224 static typename mpl::if_<
227 , Value const volatile*
231 >::type& helper(R const&);
233 BOOST_STATIC_CONSTANT(bool, value = sizeof(helper(r)) == 1);
236 template <class Reference, class Value>
237 struct is_non_proxy_reference
239 is_non_proxy_reference_impl<Reference, Value>::value
243 template <class Reference, class Value>
244 struct is_non_proxy_reference
246 typename remove_reference<Reference>::type
248 , Value const volatile*
253 // A metafunction to choose the result type of postfix ++
255 // Because the C++98 input iterator requirements say that *r++ has
256 // type T (value_type), implementations of some standard
257 // algorithms like lexicographical_compare may use constructions
262 // If *r++ returns a proxy (as required if r is writable but not
263 // multipass), this sort of expression will fail unless the proxy
264 // supports the operator<. Since there are any number of such
265 // operations, we're not going to try to support them. Therefore,
266 // even if r++ returns a proxy, *r++ will only return a proxy if
267 // *r also returns a proxy.
268 template <class Iterator, class Value, class Reference, class CategoryOrTraversal>
269 struct postfix_increment_result
272 // A proxy is only needed for readable iterators
273 is_convertible<Reference,Value>
275 // No multipass iterator can have values that disappear
276 // before positions can be re-visited
279 typename iterator_category_to_traversal<CategoryOrTraversal>::type
280 , forward_traversal_tag
285 is_non_proxy_reference<Reference,Value>
286 , postfix_increment_proxy<Iterator>
287 , writable_postfix_increment_proxy<Iterator>
289 , mpl::identity<Iterator>
293 // operator->() needs special support for input iterators to strictly meet the
294 // standard's requirements. If *i is not a reference type, we must still
295 // produce a (constant) lvalue to which a pointer can be formed. We do that by
296 // returning an instantiation of this special proxy class template.
298 struct operator_arrow_proxy
300 operator_arrow_proxy(T const* px) : m_value(*px) {}
301 const T* operator->() const { return &m_value; }
302 // This function is needed for MWCW and BCC, which won't call operator->
303 // again automatically per 13.3.1.2 para 8
304 operator const T*() const { return &m_value; }
308 // A metafunction that gets the result type for operator->. Also
309 // has a static function make() which builds the result from a
311 template <class ValueType, class Reference, class Pointer>
312 struct operator_arrow_result
314 // CWPro8.3 won't accept "operator_arrow_result::type", and we
315 // need that type below, so metafunction forwarding would be a
316 // losing proposition here.
317 typedef typename mpl::if_<
318 is_reference<Reference>
320 , operator_arrow_proxy<ValueType>
323 static type make(Reference x)
329 # if BOOST_WORKAROUND(BOOST_MSVC, <= 1200)
332 struct operator_arrow_result<int, int, int>
338 // A proxy return type for operator[], needed to deal with
339 // iterators that may invalidate referents upon destruction.
340 // Consider the temporary iterator in *(a + n)
341 template <class Iterator>
342 class operator_brackets_proxy
344 // Iterator is actually an iterator_facade, so we do not have to
345 // go through iterator_traits to access the traits.
346 typedef typename Iterator::reference reference;
347 typedef typename Iterator::value_type value_type;
350 operator_brackets_proxy(Iterator const& iter)
354 operator reference() const
359 operator_brackets_proxy& operator=(value_type const& val)
369 // A metafunction that determines whether operator[] must return a
370 // proxy, or whether it can simply return a copy of the value_type.
371 template <class ValueType, class Reference>
372 struct use_operator_brackets_proxy
375 // Really we want an is_copy_constructible trait here,
376 // but is_POD will have to suffice in the meantime.
377 boost::is_POD<ValueType>
378 , iterator_writability_disabled<ValueType,Reference>
383 template <class Iterator, class Value, class Reference>
384 struct operator_brackets_result
386 typedef typename mpl::if_<
387 use_operator_brackets_proxy<Value,Reference>
388 , operator_brackets_proxy<Iterator>
393 template <class Iterator>
394 operator_brackets_proxy<Iterator> make_operator_brackets_result(Iterator const& iter, mpl::true_)
396 return operator_brackets_proxy<Iterator>(iter);
399 template <class Iterator>
400 typename Iterator::value_type make_operator_brackets_result(Iterator const& iter, mpl::false_)
405 struct choose_difference_type
407 template <class I1, class I2>
410 # ifdef BOOST_NO_ONE_WAY_ITERATOR_INTEROP
411 iterator_difference<I1>
412 # elif BOOST_WORKAROUND(BOOST_MSVC, == 1200)
414 is_convertible<I2,I1>
415 , typename I1::difference_type
416 , typename I2::difference_type
420 is_convertible<I2,I1>
421 , iterator_difference<I1>
422 , iterator_difference<I2>
428 } // namespace detail
431 // Macros which describe the declarations of binary operators
432 # ifdef BOOST_NO_STRICT_ITERATOR_INTEROPERABILITY
433 # define BOOST_ITERATOR_FACADE_INTEROP_HEAD(prefix, op, result_type) \
435 class Derived1, class V1, class TC1, class R1, class D1 \
436 , class Derived2, class V2, class TC2, class R2, class D2 \
438 prefix typename mpl::apply2<result_type,Derived1,Derived2>::type \
440 iterator_facade<Derived1, V1, TC1, R1, D1> const& lhs \
441 , iterator_facade<Derived2, V2, TC2, R2, D2> const& rhs)
443 # define BOOST_ITERATOR_FACADE_INTEROP_HEAD(prefix, op, result_type) \
445 class Derived1, class V1, class TC1, class R1, class D1 \
446 , class Derived2, class V2, class TC2, class R2, class D2 \
448 prefix typename detail::enable_if_interoperable< \
450 , typename mpl::apply2<result_type,Derived1,Derived2>::type \
453 iterator_facade<Derived1, V1, TC1, R1, D1> const& lhs \
454 , iterator_facade<Derived2, V2, TC2, R2, D2> const& rhs)
457 # define BOOST_ITERATOR_FACADE_PLUS_HEAD(prefix,args) \
458 template <class Derived, class V, class TC, class R, class D> \
459 prefix Derived operator+ args
462 // Helper class for granting access to the iterator core interface.
464 // The simple core interface is used by iterator_facade. The core
465 // interface of a user/library defined iterator type should not be made public
466 // so that it does not clutter the public interface. Instead iterator_core_access
467 // should be made friend so that iterator_facade can access the core
468 // interface through iterator_core_access.
470 class iterator_core_access
472 # if defined(BOOST_NO_MEMBER_TEMPLATE_FRIENDS) \
473 || BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x551))
474 // Tasteless as this may seem, making all members public allows member templates
475 // to work in the absence of member template friends.
479 template <class I, class V, class TC, class R, class D> friend class iterator_facade;
481 # define BOOST_ITERATOR_FACADE_RELATION(op) \
482 BOOST_ITERATOR_FACADE_INTEROP_HEAD(friend,op, detail::always_bool2);
484 BOOST_ITERATOR_FACADE_RELATION(==)
485 BOOST_ITERATOR_FACADE_RELATION(!=)
487 BOOST_ITERATOR_FACADE_RELATION(<)
488 BOOST_ITERATOR_FACADE_RELATION(>)
489 BOOST_ITERATOR_FACADE_RELATION(<=)
490 BOOST_ITERATOR_FACADE_RELATION(>=)
491 # undef BOOST_ITERATOR_FACADE_RELATION
493 BOOST_ITERATOR_FACADE_INTEROP_HEAD(
494 friend, -, detail::choose_difference_type)
497 BOOST_ITERATOR_FACADE_PLUS_HEAD(
499 , (iterator_facade<Derived, V, TC, R, D> const&
500 , typename Derived::difference_type)
504 BOOST_ITERATOR_FACADE_PLUS_HEAD(
506 , (typename Derived::difference_type
507 , iterator_facade<Derived, V, TC, R, D> const&)
513 template <class Facade>
514 static typename Facade::reference dereference(Facade const& f)
516 return f.dereference();
519 template <class Facade>
520 static void increment(Facade& f)
525 template <class Facade>
526 static void decrement(Facade& f)
531 template <class Facade1, class Facade2>
532 static bool equal(Facade1 const& f1, Facade2 const& f2, mpl::true_)
537 template <class Facade1, class Facade2>
538 static bool equal(Facade1 const& f1, Facade2 const& f2, mpl::false_)
543 template <class Facade>
544 static void advance(Facade& f, typename Facade::difference_type n)
549 template <class Facade1, class Facade2>
550 static typename Facade1::difference_type distance_from(
551 Facade1 const& f1, Facade2 const& f2, mpl::true_)
553 return -f1.distance_to(f2);
556 template <class Facade1, class Facade2>
557 static typename Facade2::difference_type distance_from(
558 Facade1 const& f1, Facade2 const& f2, mpl::false_)
560 return f2.distance_to(f1);
564 // Curiously Recurring Template interface.
566 template <class I, class V, class TC, class R, class D>
567 static I& derived(iterator_facade<I,V,TC,R,D>& facade)
569 return *static_cast<I*>(&facade);
572 template <class I, class V, class TC, class R, class D>
573 static I const& derived(iterator_facade<I,V,TC,R,D> const& facade)
575 return *static_cast<I const*>(&facade);
579 // objects of this class are useless
580 iterator_core_access(); //undefined
584 // iterator_facade - use as a public base class for defining new
585 // standard-conforming iterators.
588 class Derived // The derived iterator type being constructed
590 , class CategoryOrTraversal
591 , class Reference = Value&
592 , class Difference = std::ptrdiff_t
594 class iterator_facade
595 # ifdef BOOST_ITERATOR_FACADE_NEEDS_ITERATOR_BASE
596 : public detail::iterator_facade_types<
597 Value, CategoryOrTraversal, Reference, Difference
599 # undef BOOST_ITERATOR_FACADE_NEEDS_ITERATOR_BASE
604 // Curiously Recurring Template interface.
608 return *static_cast<Derived*>(this);
611 Derived const& derived() const
613 return *static_cast<Derived const*>(this);
616 typedef detail::iterator_facade_types<
617 Value, CategoryOrTraversal, Reference, Difference
621 // For use by derived classes
622 typedef iterator_facade<Derived,Value,Reference,Difference> iterator_facade_;
626 typedef typename associated_types::value_type value_type;
627 typedef Reference reference;
628 typedef Difference difference_type;
629 typedef typename associated_types::pointer pointer;
630 typedef typename associated_types::iterator_category iterator_category;
632 reference operator*() const
634 return iterator_core_access::dereference(this->derived());
637 typename detail::operator_arrow_result<
644 return detail::operator_arrow_result<
648 >::make(*this->derived());
651 typename detail::operator_brackets_result<Derived,Value,reference>::type
652 operator[](difference_type n) const
654 typedef detail::use_operator_brackets_proxy<Value,Reference> use_proxy;
656 return detail::make_operator_brackets_result<Derived>(
662 Derived& operator++()
664 iterator_core_access::increment(this->derived());
665 return this->derived();
668 # if BOOST_WORKAROUND(BOOST_MSVC, == 1200)
669 typename detail::postfix_increment_result<Derived,Value,Reference,CategoryOrTraversal>::type
672 typename detail::postfix_increment_result<Derived,Value,Reference,CategoryOrTraversal>::type
673 tmp(this->derived());
679 Derived& operator--()
681 iterator_core_access::decrement(this->derived());
682 return this->derived();
685 Derived operator--(int)
687 Derived tmp(this->derived());
692 Derived& operator+=(difference_type n)
694 iterator_core_access::advance(this->derived(), n);
695 return this->derived();
698 Derived& operator-=(difference_type n)
700 iterator_core_access::advance(this->derived(), -n);
701 return this->derived();
704 Derived operator-(difference_type x) const
706 Derived result(this->derived());
710 # if BOOST_WORKAROUND(BOOST_MSVC, <= 1200)
711 // There appears to be a bug which trashes the data of classes
712 // derived from iterator_facade when they are assigned unless we
713 // define this assignment operator. This bug is only revealed
714 // (so far) in STLPort debug mode, but it's clearly a codegen
715 // problem so we apply the workaround for all MSVC6.
716 iterator_facade& operator=(iterator_facade const&)
723 # if !BOOST_WORKAROUND(BOOST_MSVC, == 1200)
724 template <class I, class V, class TC, class R, class D>
725 typename detail::postfix_increment_result<I,V,R,TC>::type
727 iterator_facade<I,V,TC,R,D>& i
731 typename detail::postfix_increment_result<I,V,R,TC>::type
732 tmp(*static_cast<I*>(&i));
742 // Comparison operator implementation. The library supplied operators
743 // enables the user to provide fully interoperable constant/mutable
744 // iterator types. I.e. the library provides all operators
745 // for all mutable/constant iterator combinations.
747 // Note though that this kind of interoperability for constant/mutable
748 // iterators is not required by the standard for container iterators.
749 // All the standard asks for is a conversion mutable -> constant.
750 // Most standard library implementations nowadays provide fully interoperable
751 // iterator implementations, but there are still heavily used implementations
752 // that do not provide them. (Actually it's even worse, they do not provide
753 // them for only a few iterators.)
755 // ?? Maybe a BOOST_ITERATOR_NO_FULL_INTEROPERABILITY macro should
756 // enable the user to turn off mixed type operators
758 // The library takes care to provide only the right operator overloads.
761 // bool operator==(Iterator, Iterator);
762 // bool operator==(ConstIterator, Iterator);
763 // bool operator==(Iterator, ConstIterator);
764 // bool operator==(ConstIterator, ConstIterator);
768 // In order to do so it uses c++ idioms that are not yet widely supported
769 // by current compiler releases. The library is designed to degrade gracefully
770 // in the face of compiler deficiencies. In general compiler
771 // deficiencies result in less strict error checking and more obscure
772 // error messages, functionality is not affected.
774 // For full operation compiler support for "Substitution Failure Is Not An Error"
775 // (aka. enable_if) and boost::is_convertible is required.
777 // The following problems occur if support is lacking.
782 // AdaptorA<Iterator1> a1;
783 // AdaptorA<Iterator2> a2;
785 // // This will result in a no such overload error in full operation
786 // // If enable_if or is_convertible is not supported
787 // // The instantiation will fail with an error hopefully indicating that
788 // // there is no operator== for Iterator1, Iterator2
789 // // The same will happen if no enable_if is used to remove
790 // // false overloads from the templated conversion constructor
796 // AdaptorA<Iterator> a;
797 // AdaptorB<Iterator> b;
799 // // This will result in a no such overload error in full operation
800 // // If enable_if is not supported the static assert used
801 // // in the operator implementation will fail.
802 // // This will accidently work if is_convertible is not supported.
808 # ifdef BOOST_NO_ONE_WAY_ITERATOR_INTEROP
809 # define BOOST_ITERATOR_CONVERTIBLE(a,b) mpl::true_()
811 # define BOOST_ITERATOR_CONVERTIBLE(a,b) is_convertible<a,b>()
814 # define BOOST_ITERATOR_FACADE_INTEROP(op, result_type, return_prefix, base_op) \
815 BOOST_ITERATOR_FACADE_INTEROP_HEAD(inline, op, result_type) \
817 /* For those compilers that do not support enable_if */ \
818 BOOST_STATIC_ASSERT(( \
819 is_interoperable< Derived1, Derived2 >::value \
821 return_prefix iterator_core_access::base_op( \
822 *static_cast<Derived1 const*>(&lhs) \
823 , *static_cast<Derived2 const*>(&rhs) \
824 , BOOST_ITERATOR_CONVERTIBLE(Derived2,Derived1) \
828 # define BOOST_ITERATOR_FACADE_RELATION(op, return_prefix, base_op) \
829 BOOST_ITERATOR_FACADE_INTEROP( \
831 , detail::always_bool2 \
836 BOOST_ITERATOR_FACADE_RELATION(==, return, equal)
837 BOOST_ITERATOR_FACADE_RELATION(!=, return !, equal)
839 BOOST_ITERATOR_FACADE_RELATION(<, return 0 >, distance_from)
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 # undef BOOST_ITERATOR_FACADE_RELATION
845 // operator- requires an additional part in the static assertion
846 BOOST_ITERATOR_FACADE_INTEROP(
848 , detail::choose_difference_type
852 # undef BOOST_ITERATOR_FACADE_INTEROP
853 # undef BOOST_ITERATOR_FACADE_INTEROP_HEAD
855 # define BOOST_ITERATOR_FACADE_PLUS(args) \
856 BOOST_ITERATOR_FACADE_PLUS_HEAD(inline, args) \
858 Derived tmp(static_cast<Derived const&>(i)); \
862 BOOST_ITERATOR_FACADE_PLUS((
863 iterator_facade<Derived, V, TC, R, D> const& i
864 , typename Derived::difference_type n
867 BOOST_ITERATOR_FACADE_PLUS((
868 typename Derived::difference_type n
869 , iterator_facade<Derived, V, TC, R, D> const& i
871 # undef BOOST_ITERATOR_FACADE_PLUS
872 # undef BOOST_ITERATOR_FACADE_PLUS_HEAD
876 #include <boost/iterator/detail/config_undef.hpp>
878 #endif // BOOST_ITERATOR_FACADE_23022003THW_HPP