asvanberg opened a new pull request, #684:
URL: https://github.com/apache/wicket/pull/684
Wicket currently leaves a lot to be desired when working with polymorphic
datastructures.
Consider the following scenario:
```java
interface TextMatchingService {
sealed interface Status {
record NotSubmitted(Runnable submit) implements Status {}
record Queued(Instant since, Optional<Instant> expectedFinish)
implements Status {}
record Analysed(float percentMatch) implements Status {}
record Error(int errorCode, String humanReadableMessage) implements
Status {}
}
Status getStatus(File file);
}
```
Now I want to have a panel that gets the status of a file and then,
depending on the status, shows the different cases.
If I were to unpack the model and `switch` over the type in the constructor,
when the value returned by the `IModel<Status>` changes due to the asynchronous
nature of the text matching the hierarchy would be out of sync.
The proposed `poly` function would enable the following pattern for dealing
with this case.
```java
public class TextMatchingPanel extends GenericPanel<File> {
@Inject
TextMatchingService textMatchingService;
public TextMatchingPanel(String id, IModel<File> fileModel) {
super(id, fileModel);
IModel<Status> statusModel =
fileModel.map(textMatchingService::getStatus);
add(new NotSubmittedPanel("not_submitted",
statusModel.poly(NotSubmitted.class));
[add more specific status panels]
}
class NotSubmittedPanel extends Panel {
NotSubmittedPanel(String id, IModel<NotSubmitted> notSubmittedModel) {
super(id, notSubmittedModel);
add(new Link<>("submit") {
@Override
public void onClick() {
NotSubmitted notSubmitted = notSubmittedModel.getObject();
Runnable submitForTextMatching = notSubmitted.submit();
submitForTextMatching.run();
}
});
}
@Override
protected void onConfigure() {
super.onConfigure();
setVisible(getDefaultModelObject() != null);
}
}
[more status panels]
}
```
If there's a better way to do this, preferably using switch expressions (to
get totality checking), that would be preferred but I've yet to come up with
one.
Unpacking in the constructor and creating different component hierarchies
would work if the page was stateless but then there would also be no need for a
detachable `IModel` since nothing gets serialized.
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