A feedstock line comprises elongate filaments, a resin, and a full-length optical waveguide, comprising a full-length optical core. The full-length optical waveguide is configured such that when electromagnetic radiation enters the full-length optical core via at least one of a first full-length-optical-core end face, a second full-length-optical-core end face, or a full-length peripheral surface that extends between the first full-length-optical-core end face and the second full-length-optical-core end face, at least a portion of the electromagnetic radiation exits the full-length optical core via the full-length peripheral surface to irradiate, in an interior volume of the feedstock line, the resin that, due at least in part to the elongate filaments, is not directly accessible to the electromagnetic radiation, incident on the exterior surface of the feedstock line.