So far, we've been using the syntax:

double_ >> *(',' >> double_)

to parse a comma-delimited list of numbers. Such lists are common in parsing and Spirit provides a simpler shortcut for them. The expression above can be simplified to:

double_ % ','

read as: a list of doubles separated by ','.

This sample, again a variation of our previous example, demonstrates just that:

template <typename Iterator>
bool parse_numbers(Iterator first, Iterator last, std::vector<double>& v)
{
    using x3::double_;
    using x3::phrase_parse;
    using x3::_attr;
    using ascii::space;

    auto push_back = [&](auto& ctx){ v.push_back(_attr(ctx)); };

    bool r = phrase_parse(first, last,

        //  Begin grammar
        (
            double_[push_back] % ','
        )
        ,
        //  End grammar

        space);

    if (first != last) // fail if we did not get a full match
        return false;
    return r;
}

The full cpp file for this example can be found here: num_list3.cpp