ForwardIterator -> ReadableIteratorConcept & ForwardTraversalConcept

The concept of ForwardIterator is flawed because it mixed 2 sets of concepts (value access and traversal) into 1 package.

http://www.boost.org/doc/libs/1_65_1/libs/iterator/doc/new-iter-concepts.html

It requires value_type (const)& as return type when dereference is applied, which is not mandatory in spirit parsing. A return type which is convertible to value_type is good enough. ReadableIteratorConcept and ForwardTraversalConcept should be what we need for the iterator check.

For example, the iterator of the range returned by boost::adaptors::transform(std::string, func) is normally not a ForwardIterator. But it fulfills ReadableIteratorConcept and ForwardTraversalConcept and should be able to be parsed by spirit.

include/boost/spirit/home/qi/parse.hpp

@@ -15,7 +15,7 @@
 #include <boost/spirit/home/support/context.hpp>
 #include <boost/spirit/home/support/nonterminal/locals.hpp>
 #include <boost/spirit/home/qi/detail/parse.hpp>
-#include <boost/concept_check.hpp>
+#include <boost/iterator/iterator_concepts.hpp>
 
 namespace boost { namespace spirit { namespace qi
 {
@@ -27,11 +27,12 @@ namespace boost { namespace spirit { namespace qi
       , Iterator last
       , Expr const& expr)
     {
-        // Make sure the iterator is at least a forward_iterator. If you got a 
-        // compilation error here, then you are using an input_iterator while
-        // calling this function, you need to supply at least a 
-        // forward_iterator instead.
-        BOOST_CONCEPT_ASSERT((ForwardIterator<Iterator>));
+        // Make sure the iterator is at least a readable forward traversal iterator.
+        // If you got a compilation error here, then you are using a weaker iterator
+        // while calling this function, you need to supply a readable forward traversal
+        // iterator instead.
+        BOOST_CONCEPT_ASSERT((boost_concepts::ReadableIteratorConcept<Iterator>));
+        BOOST_CONCEPT_ASSERT((boost_concepts::ForwardTraversalConcept<Iterator>));
 
         return detail::parse_impl<Expr>::call(first, last, expr);
     }
@@ -71,11 +72,12 @@ namespace boost { namespace spirit { namespace qi
       , Expr const& expr
       , Attr& attr)
     {
-        // Make sure the iterator is at least a forward_iterator. If you got a 
-        // compilation error here, then you are using an input_iterator while
-        // calling this function, you need to supply at least a 
-        // forward_iterator instead.
-        BOOST_CONCEPT_ASSERT((ForwardIterator<Iterator>));
+        // Make sure the iterator is at least a readable forward traversal iterator.
+        // If you got a compilation error here, then you are using a weaker iterator
+        // while calling this function, you need to supply a readable forward traversal
+        // iterator instead.
+        BOOST_CONCEPT_ASSERT((boost_concepts::ReadableIteratorConcept<Iterator>));
+        BOOST_CONCEPT_ASSERT((boost_concepts::ForwardTraversalConcept<Iterator>));
 
         // Report invalid expression error as early as possible.
         // If you got an error_invalid_expression error message here,
@@ -108,11 +110,12 @@ namespace boost { namespace spirit { namespace qi
       , Skipper const& skipper
       , BOOST_SCOPED_ENUM(skip_flag) post_skip = skip_flag::postskip)
     {
-        // Make sure the iterator is at least a forward_iterator. If you got a 
-        // compilation error here, then you are using an input_iterator while
-        // calling this function, you need to supply at least a 
-        // forward_iterator instead.
-        BOOST_CONCEPT_ASSERT((ForwardIterator<Iterator>));
+        // Make sure the iterator is at least a readable forward traversal iterator.
+        // If you got a compilation error here, then you are using a weaker iterator
+        // while calling this function, you need to supply a readable forward traversal
+        // iterator instead.
+        BOOST_CONCEPT_ASSERT((boost_concepts::ReadableIteratorConcept<Iterator>));
+        BOOST_CONCEPT_ASSERT((boost_concepts::ForwardTraversalConcept<Iterator>));
 
         return detail::phrase_parse_impl<Expr>::call(
             first, last, expr, skipper, post_skip);
@@ -142,11 +145,12 @@ namespace boost { namespace spirit { namespace qi
       , BOOST_SCOPED_ENUM(skip_flag) post_skip
       , Attr& attr)
     {
-        // Make sure the iterator is at least a forward_iterator. If you got a 
-        // compilation error here, then you are using an input_iterator while
-        // calling this function, you need to supply at least a 
-        // forward_iterator instead.
-        BOOST_CONCEPT_ASSERT((ForwardIterator<Iterator>));
+        // Make sure the iterator is at least a readable forward traversal iterator.
+        // If you got a compilation error here, then you are using a weaker iterator
+        // while calling this function, you need to supply a readable forward traversal
+        // iterator instead.
+        BOOST_CONCEPT_ASSERT((boost_concepts::ReadableIteratorConcept<Iterator>));
+        BOOST_CONCEPT_ASSERT((boost_concepts::ForwardTraversalConcept<Iterator>));
 
         // Report invalid expression error as early as possible.
         // If you got an error_invalid_expression error message here,

include/boost/spirit/home/x3/core/parse.hpp

@@ -10,7 +10,7 @@
 #include <boost/spirit/home/x3/support/context.hpp>
 #include <boost/spirit/home/x3/core/parser.hpp>
 #include <boost/spirit/home/x3/core/skip_over.hpp>
-#include <boost/concept_check.hpp>
+#include <boost/iterator/iterator_concepts.hpp>
 
 namespace boost { namespace spirit { namespace x3
 {
@@ -23,11 +23,12 @@ namespace boost { namespace spirit { namespace x3
       , Parser const& p
       , Attribute& attr)
     {
-        // Make sure the iterator is at least a forward_iterator. If you got a
-        // compilation error here, then you are using an input_iterator while
-        // calling this function. You need to supply at least a forward_iterator
-        // instead.
-        BOOST_CONCEPT_ASSERT((ForwardIterator<Iterator>));
+        // Make sure the iterator is at least a readable forward traversal iterator.
+        // If you got a compilation error here, then you are using a weaker iterator
+        // while calling this function, you need to supply a readable forward traversal
+        // iterator instead.
+        BOOST_CONCEPT_ASSERT((boost_concepts::ReadableIteratorConcept<Iterator>));
+        BOOST_CONCEPT_ASSERT((boost_concepts::ForwardTraversalConcept<Iterator>));
 
         // If you get an error no matching function for call to 'as_parser'
         // here, then p is not a parser or there is no suitable conversion
@@ -101,11 +102,12 @@ namespace boost { namespace spirit { namespace x3
       , Attribute& attr
       , skip_flag post_skip = skip_flag::post_skip)
     {
-        // Make sure the iterator is at least a forward_iterator. If you got a
-        // compilation error here, then you are using an input_iterator while
-        // calling this function. You need to supply at least a forward_iterator
-        // instead.
-        BOOST_CONCEPT_ASSERT((ForwardIterator<Iterator>));
+        // Make sure the iterator is at least a readable forward traversal iterator.
+        // If you got a compilation error here, then you are using a weaker iterator
+        // while calling this function, you need to supply a readable forward traversal
+        // iterator instead.
+        BOOST_CONCEPT_ASSERT((boost_concepts::ReadableIteratorConcept<Iterator>));
+        BOOST_CONCEPT_ASSERT((boost_concepts::ForwardTraversalConcept<Iterator>));
 
         static_assert(!std::is_same<Skipper, unused_type>::value,
             "Error! Skipper cannot be unused_type.");

test/qi/Jamfile

@@ -123,6 +123,7 @@ run utree1.cpp ;
 run utree2.cpp ;
 run utree3.cpp ;
 run utree4.cpp ;
+run iterator_check.cpp ;
 
 compile pass_container3.cpp ;
 compile regression_attr_with_action.cpp ;

test/qi/iterator_check.cpp

@@ -0,0 +1,52 @@
+/*=============================================================================
+    Copyright (c) 2001-2017 Joel de Guzman
+    Copyright (c) 2017 think-cell GmbH
+
+    Distributed under the Boost Software License, Version 1.0. (See accompanying
+    file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+=============================================================================*/
+#include <boost/detail/lightweight_test.hpp>
+#include <boost/spirit/home/qi.hpp>
+#include <boost/range/adaptor/transformed.hpp>
+
+#include <iostream>
+#include <string>
+#include <functional>
+
+namespace {
+    char transform_func(char c) {
+        return c < 'a' || 'z' < c ? c : static_cast<char>(c - 'a' + 'A');
+    }
+}
+
+int main()
+{
+    using boost::adaptors::transform;
+    using boost::spirit::qi::raw;
+    using boost::spirit::qi::eps;
+    using boost::spirit::qi::eoi;
+    using boost::spirit::qi::upper;
+    using boost::spirit::qi::repeat;
+    using boost::spirit::qi::parse;
+
+    std::string input = "abcde";
+    boost::transformed_range<char(*)(char), std::string> const rng = transform(input, transform_func);
+
+    {
+        std::string str;
+        BOOST_TEST((parse(boost::begin(rng), boost::end(rng), +upper >> eoi, str)));
+        BOOST_TEST(("ABCDE"==str));
+    }
+
+    {
+        boost::iterator_range<boost::range_iterator<boost::transformed_range<char(*)(char), std::string> const>::type> str;
+        BOOST_TEST((parse(boost::begin(rng), boost::end(rng), raw[+upper >> eoi], str)));
+        BOOST_TEST((boost::equal(std::string("ABCDE"), str)));
+    }
+
+    {
+        BOOST_TEST((parse(boost::begin(rng), boost::end(rng), (repeat(6)[upper] | repeat(5)[upper]) >> eoi)));
+    }
+
+    return boost::report_errors();
+}

test/x3/Jamfile

@@ -117,3 +117,4 @@ run seek.cpp ;
 
 run x3_variant.cpp ;
 run error_handler.cpp /boost//system /boost//filesystem ;
+run iterator_check.cpp ;

test/x3/iterator_check.cpp

@@ -0,0 +1,49 @@
+/*=============================================================================
+    Copyright (c) 2001-2017 Joel de Guzman
+    Copyright (c) 2017 think-cell GmbH
+
+    Distributed under the Boost Software License, Version 1.0. (See accompanying
+    file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+=============================================================================*/
+#include <boost/detail/lightweight_test.hpp>
+#include <boost/spirit/home/x3.hpp>
+#include <boost/range/adaptor/transformed.hpp>
+
+#include <iostream>
+#include <string>
+#include <functional>
+
+int main()
+{
+    using boost::adaptors::transform;
+    using boost::spirit::x3::raw;
+    using boost::spirit::x3::eps;
+    using boost::spirit::x3::eoi;
+    using boost::spirit::x3::upper;
+    using boost::spirit::x3::repeat;
+    using boost::spirit::x3::parse;
+
+    std::string input = "abcde";
+    std::function<char(char)> func = [](char c) {
+        return c < 'a' || 'z' < c ? c : static_cast<char>(c - 'a' + 'A');
+    };
+    auto const rng = transform(input, func);
+
+    {
+        std::string str;
+        BOOST_TEST((parse(boost::begin(rng), boost::end(rng), +upper >> eoi, str)));
+        BOOST_TEST(("ABCDE"==str));
+    }
+
+    {
+        boost::iterator_range<decltype(boost::begin(rng))> str;
+        BOOST_TEST((parse(boost::begin(rng), boost::end(rng), raw[+upper >> eoi], str)));
+        BOOST_TEST((boost::equal(std::string("ABCDE"), str)));
+    }
+
+    {
+        BOOST_TEST((parse(boost::begin(rng), boost::end(rng), (repeat(6)[upper] | repeat(5)[upper]) >> eoi)));
+    }
+
+    return boost::report_errors();
+}