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https://issues.apache.org/jira/browse/WICKET-2137?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12679018#action_12679018
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omichallat edited comment on WICKET-2137 at 3/4/09 5:02 PM:
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Brill, James is right, the new signature will accept an IModel<List<Integer>>.
This takes care of not pushing the wildcard onto the caller.
As for the "read-only" problem, it can easily be solved with a private helper
method that captures the wildcard.
Here is another example:
// Simulates the DropDownChoice with the change suggested by James
static class DropDownChoiceWidened<T> {
// Just an artifact to simulate getModelObject
private IModel<? extends List<? extends T>> model;
// The new constructor with widened type
public DropDownChoiceWidened(String id, IModel<? extends List<? extends
T>> model) {
this.model = model;
}
// The getModelObject inherited from FormComponent would have this
signature:
public List<? extends T> getModelObject() { return this.model.getObject(); }
}
// intModel is the same as in my previous example (an IModel<List<Integer>>)
// Now the constructor invocation compiles:
new DropDownChoiceWidened<Number>("id", intModel) {
// Should the component need to mutate the list:
public void someMethodThatNeedsToRemoveElements() {
safeRemove(this.getModelObject(), 1);
}
// Private helper that captures the wildcard
private <T extends Number> void safeRemove(List<T> list, int index) {
// List<T> is not read-only
list.remove(index);
}
};
My vote changes in favor of James' widened wildcard.
was (Author: omichallat):
Brill, James is right, the new signature will accept an
IModel<List<Integer>>. This takes care of not pushing the wildcard onto the
caller.
As for the "read-only" problem, it can easily be solved with a private helper
method that captures the wildcard.
Here is another example:
// Simulates the DropDownChoice with the change suggested by James
static class DropDownChoiceWidened<T> {
// Just an artifact to simulate getModelObject
private IModel<? extends List<? extends T>> model;
// The new constructor with widened type
public DropDownChoiceWidened(String id, IModel<? extends List<? extends
T>> model) {
this.model = model;
}
// The getModelObject inherited from FormComponent would have this
signature:
public List<? extends T> getModelObject() { return this.model.getObject(); }
}
// intModel is the same as in my previous example (an IModel<List<Integer>>)
// Now the constructor invocation compiles:
new DropDownChoiceWidened<Number>("id", intModel) {
// Should the component need to mutate the list:
public void someMethodThatNeedsToRemoveElements() {
safeRemove(this.getModelObject(), 1);
}
// Private helper that captures the wildcard
private <T extends Number> void safeRemove(List<T> list, int index) {
// List<T> is not read-only
list.remove(index);
}
};
Thanks to James' suggestion, I now agree with a wildcard type.
> Remove ? extends from constructor of DropDownChoice
> ---------------------------------------------------
>
> Key: WICKET-2137
> URL: https://issues.apache.org/jira/browse/WICKET-2137
> Project: Wicket
> Issue Type: Improvement
> Components: wicket
> Affects Versions: 1.4-RC3
> Environment: 1.4-SNAPSHOT as of 2009-01-28
> Reporter: Brill Pappin
> Attachments: TestGenerics.java
>
>
> DropDownChoice has a generics definition of List<? extends T> in its
> constructor.
> This causes trouble with existing models that may be used in a DropDownChoice
> and is not consistant with ListView which uses <List<T>>.
> Change DropDownChoice to match the other list type components so that their
> models can be used across components.
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