private String validComponents(Map<String, TYPE> components) {
        List<String> componentIds = new ArrayList<>();
        components.forEach((key, value) -> componentIds.add(key));
        componentIds.sort(null);
        return String.join(", ", componentIds);
    }
A collection of components of a single type, of which one is selected.

@author bratseth
indexinglanguage/src/main/java/com/yahoo/vespa/indexinglanguage/expressions/SelectedComponent.java