class TraitUtil {
    
    /**
     * Returns a view of the specified document that implements the specified
     * trait. The returned document might or might not be the same instance as
     * was inputted to this method. If not, the instance will be initialized
     * using the specified constructor.
     * 
     * @param <TRAIT>      the trait class
     * @param document     the document to create a view of
     * @param trait        the trait type
     * @param constructor  constructor to use for documents that lack the trait
     * @return             the view of the trait
     */
    public static <TRAIT extends Document> TRAIT viewOf(
            Document document,
            Class<TRAIT> trait,
            TraitViewConstructor<? extends TRAIT> constructor) {<FILL_FUNCTION_BODY>}
    
    /**
     * A functional interface describing the constructor for a class that
     * implements a specific trait.
     * 
     * @param <TRAIT>  the trait to construct an implementation of
     */
    @FunctionalInterface
    public interface TraitViewConstructor<TRAIT> {
        TRAIT create(Document parent, Map<String, Object> data, Class<? extends Document> mainInterface);
    }
    
    /**
     * Utility classes should not be instantiated.
     */
    private TraitUtil() {
        throw new UnsupportedOperationException();
    }
}

        
        if (trait.isInstance(document)) {
            return trait.cast(document);
        } else {
            
            final Class<? extends Document> mainInterface;
            
            if (document instanceof HasMainInterface) {
                mainInterface = ((HasMainInterface) document).mainInterface();
            } else {
                mainInterface = trait;
            }
            
            return constructor.create(
                document.getParent().orElse(null), 
                document.getData(),
                mainInterface
            );
        }
    
<no_super_class>