def actualize_sources (self, sources, prop_set):
        """ Creates actual jam targets for sources. Initializes two member
            variables:
            'self.actual_sources_' -- sources which are passed to updating action
            'self.dependency_only_sources_' -- sources which are made dependencies, but
            are not used otherwise.

            New values will be *appended* to the variables. They may be non-empty,
            if caller wants it.
        """
        assert is_iterable_typed(sources, VirtualTarget)
        assert isinstance(prop_set, property_set.PropertySet)
        dependencies = self.properties_.get ('<dependency>')

        self.dependency_only_sources_ += self.actualize_source_type (dependencies, prop_set)
        self.actual_sources_ += self.actualize_source_type (sources, prop_set)

        # This is used to help bjam find dependencies in generated headers
        # in other main targets.
        # Say:
        #
        #   make a.h : ....... ;
        #   exe hello : hello.cpp : <implicit-dependency>a.h ;
        #
        # However, for bjam to find the dependency the generated target must
        # be actualized (i.e. have the jam target). In the above case,
        # if we're building just hello ("bjam hello"), 'a.h' won't be
        # actualized unless we do it here.
        implicit = self.properties_.get("<implicit-dependency>")

        for i in implicit:
            i.actualize()