1[/============================================================================== 2 Copyright (C) 2001-2015 Joel de Guzman 3 Copyright (C) 2001-2011 Hartmut Kaiser 4 5 Distributed under the Boost Software License, Version 1.0. (See accompanying 6 file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) 7===============================================================================/] 8 9[section Number List Attribute - one more, with style] 10 11You've seen that the `double_` parser has a `double` attribute. All parsers have 12an attribute, even complex parsers. Those that are composed from primitives 13using operators, like the list parser, also have an attribute. It so happens that 14the attribute of a list parser: 15 16 p % d 17 18is a `std::vector` of the attribute of `p`. So, for our parser: 19 20 21 double_ % ',' 22 23we'll have an attribute of: 24 25 std::vector<double> 26 27So, what does this give us? Well, we can simply pass in a `std::vector<double>` 28to our number list parser and it will happily churn out our result in our 29vector. For that to happen, we'll use a variation of the `phrase_parse` with 30an additional argument: the parser's attribute. With the following arguments 31passed to `phrase_parse` 32 33# An iterator pointing to the start of the input 34# An iterator pointing to one past the end of the input 35# The parser object 36# Another parser called the skip parser 37# The parser's attribute 38 39Our parser now is further simplified to: 40 41 template <typename Iterator> 42 bool parse_numbers(Iterator first, Iterator last, std::vector<double>& v) 43 { 44 using x3::double_; 45 using x3::phrase_parse; 46 using x3::_attr; 47 using ascii::space; 48 49 bool r = phrase_parse(first, last, 50 51 // Begin grammar 52 ( 53 double_ % ',' 54 ) 55 , 56 // End grammar 57 58 space, v); 59 60 if (first != last) // fail if we did not get a full match 61 return false; 62 return r; 63 } 64 65The full cpp file for this example can be found here: 66[@../../../example/x3/num_list/num_list4.cpp num_list4.cpp] 67 68[*Hey, no more actions!!!] Now we're entering the realm of attribute grammars. 69Cool eh? 70 71[endsect] 72