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I'm using Wicket 6/Java 8 and am adding some simple classes that make use of the lambda functionality from Java 8 (I know the later versions of Wicket have lambda support but we can't upgrade right now). I'm creating a LambdaModel that is a bit like the PropertyModel, which I'm hoping will remove the need to hardcode Strings representing the nested path to the property.

To start, I'm making a simple readonly version. Ive made Serializable versions of the Function interface to create the following:

public class LambdaModelUtils {
  public static <X,R> IModel<R> ofNested( IModel<X> target, SerializableFunction<?,?>... path ) {
     // creates a model that works through each function in the path in turn
My implementation works well, but the only problem is that calling this method the 'efficient' way causes compile errors:
IModel<Parent> parentModel = ...
IModel<String> model = LambdaModelUtils.ofNested( parentModel,
                            Parent::getChild, Child::getName );  // Compile time error
The only way I can find to call the method is by the following:
SerializableFunction<Parent,Child> path0 = Parent::getChild;
SerializableFunction<Child,String> path1 = Child::getName;
IModel<String> model = LambdaModelUtils.ofNested( parentModel,
                            path0, path1 );  // works
This is a bit clumsy - is there a better way?
Ive looked here but this doesnt seem to work either:
List<SerializableFunction> path = Arrays.asList( Parent::getChild, Child::getName );
Thanks
                Just curious... Why shouldn't you use lambda expressions where you're using method references?
– ernest_k
                May 18, 2018 at 9:13
                Since SerializableFunction<?,?> would need unchecked casts to use, it is not better than using strings to represent properties, i.e. no compile-time safety at all.
– Holger
                May 18, 2018 at 9:42
If you're using these functions to get to a nested property, but don't really use the intermediate results, I'd advice you to just use a lambda expression:
public static <X,R> IModel<R> ofNested(IModel<X> target, SerializableFunction<X, R> path)
IModel<Parent> parentModel = ...
IModel<String> model = LambdaModelUtils.ofNested(parentModel, p -> p.getChild().getName());
This works since the target type of the lambda is now known, instead of the generic SerializedFunction<?, ?>, you get SerialiedFunction<X, R> where X = Parent and R = String.
I tried something similar to your code. Casting the method references to the functional interface type solves the compilation error:
IModel<String> model =
    LambdaModelUtils.ofNested(parentModel,
                             (SerializableFunction<Parent,Child>) Parent::getChild, 
                             (SerializableFunction<Child,String>) Child::getName);
Not the prettiest solution, but at least it saves you the need to declare the path0 and path1 variables.
        
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