From a24bdfbbb19015717e7cbb6ccef138a02dddef6e Mon Sep 17 00:00:00 2001
From: Egor Derevenetc <ederevenetc@think-cell.com>
Date: Tue, 7 Feb 2017 14:01:05 +0100
Subject: [PATCH] Weaken iterator requirements in qi::parse and
 qi::phrase_parse

Iterator used for parsing does not need to fulfil all requirements of
ForwardIterator. In particular, it is fine if *it has value_type and not
reference type.
---
 include/boost/spirit/home/qi/parse.hpp | 45 +++++++++++++++++++---------------
 1 file changed, 25 insertions(+), 20 deletions(-)

diff --git a/include/boost/spirit/home/qi/parse.hpp b/include/boost/spirit/home/qi/parse.hpp
index 261df759cc..5f7d6d4c51 100644
--- a/include/boost/spirit/home/qi/parse.hpp
+++ b/include/boost/spirit/home/qi/parse.hpp
@@ -16,6 +16,7 @@
 #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 +28,12 @@ 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 single pass 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 single pass
+        // iterator instead.
+        BOOST_CONCEPT_ASSERT((boost_concepts::ReadableIteratorConcept<Iterator>));
+        BOOST_CONCEPT_ASSERT((boost_concepts::SinglePassIteratorConcept<Iterator>));
 
         return detail::parse_impl<Expr>::call(first, last, expr);
     }
@@ -71,11 +73,12 @@ 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 single pass 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 single pass
+        // iterator instead.
+        BOOST_CONCEPT_ASSERT((boost_concepts::ReadableIteratorConcept<Iterator>));
+        BOOST_CONCEPT_ASSERT((boost_concepts::SinglePassIteratorConcept<Iterator>));
 
         // Report invalid expression error as early as possible.
         // If you got an error_invalid_expression error message here,
@@ -108,11 +111,12 @@ 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 single pass 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 single pass
+        // iterator instead.
+        BOOST_CONCEPT_ASSERT((boost_concepts::ReadableIteratorConcept<Iterator>));
+        BOOST_CONCEPT_ASSERT((boost_concepts::SinglePassIteratorConcept<Iterator>));
 
         return detail::phrase_parse_impl<Expr>::call(
             first, last, expr, skipper, post_skip);
@@ -142,11 +146,12 @@ 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 single pass 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 single pass
+        // iterator instead.
+        BOOST_CONCEPT_ASSERT((boost_concepts::ReadableIteratorConcept<Iterator>));
+        BOOST_CONCEPT_ASSERT((boost_concepts::SinglePassIteratorConcept<Iterator>));
 
         // Report invalid expression error as early as possible.
         // If you got an error_invalid_expression error message here,