How to force attribute propagation in x3 when using semantic actions

Hi,

I am just learning Spirit and x3.  In my test, I parse a list of numbers
into a custom type resembling std::complex (just a pair of numbers).

Using BOOST_FUSION_ADAPT_STRUCT works just fine, but I am testing what
happens when I fill each structure by means of semantic actions.  In
that case, I have to keep specifying manually the return value of each
rule, not only the one with semantic actions.

I have read that this is solved in Qi using the %= operator, but I do
not know how to do the same in x3.

Here is my rule definitions, just a modification of the first part of
the calc example:

    namespace calculator_grammar
    {
		using x3::double_;
		using x3::_val;
		using x3::_attr;

//		My custom type
		struct comptype{
			double a, b;
		};

		// This is the list rule aggregating the comptypes, but it only
		// works if I specify the result type (std::vector<comptype>)

		x3::rule<class _//, std::vector<comptype>, true
				 > const complist("complist");

        // Semantic actions for filling the struct.
		auto filla = [](auto & ctx){_val(ctx).a = _attr(ctx);};
		auto fillb = [](auto & ctx){_val(ctx).b = _attr(ctx);};
		
        // Specifying the return type just in this rule is fine by me,
        // but I gues it does not have any effect whatsoever.
        auto const mycomp =
			x3::rule<class _, comptype>{"my comp parser"}=
			x3::lit('(') >>
			double_[filla] >> ',' >>
			double_[fillb]>> ')'
            ;

        // Let us pretend that this parses a list and not only two entities.
		auto const complist_def =
			mycomp >> "," >> mycomp;
		
        BOOST_SPIRIT_DEFINE(
			complist
        );

        auto calculator = complist;
    }

    using calculator_grammar::calculator;
}

How can I stop having to accumulate rule results (std::vector<...>) in
the definition of rules based on "mycomp"?

Thanks!

-- 
Alberto


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