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Support for generic types in containers #1401

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merged 2 commits into from
Feb 10, 2022

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mgorniew
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@mgorniew mgorniew commented Aug 2, 2021

Improvement for issue #1396. This will also add CommandLine.UseDefaultConverter which can be used as marker for default converter fallback.

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@remkop remkop left a comment

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Sorry for the very long delay. I finally have some time to look at picocli again.

I am okay to merge this PR, but I would prefer not to include the UseDefaultConverter API.
Can you take a look and let me know what you think?

*
* Instances of this class will throw UnsupportedOperationException for {@link #convert(String)} method.
*/
public static final class UseDefaultConverter implements ITypeConverter<Object> {
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Do we need to introduce this UseDefaultConverter class as part of this PR?
Applications can use the CommandLine::registerConverter method:

new CommandLine(new MyApp())
    .registerConverter(GenericValue.class, GenericValueConverter.class)
    .execute(args);

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UseDefaultConverter is only for use cases when we need to provide converters for multiple parameters and for some of them we simple want to use default, e.g.:

           @Option(names = "-D", converter = {UseDefaultConverter.class, GenericValueConverter.class})
            Map<String, GenericValue<?>> values;

In this case I would need to provided custom convert for String class also since BuiltIt.StringConverter is private.

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I understand that. Is there any issue with using the CommandLine::registerConverter method to register the GenericValueConverter?

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@mgorniew mgorniew Nov 26, 2021

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With global registration there may be issue with type erasure. If I want to use two different converters for same GenericValue<T> (e.g. in one parameter GenericValue<Integer> and in other GenericValue<String>) then I won't be able to this with CommandLine::registerConverter

@remkop remkop linked an issue Nov 25, 2021 that may be closed by this pull request
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remkop commented Nov 29, 2021

Okay, I see now, thanks for the clarification.

Without the UseDefaultConverter, this PR can be part of the next bugfix release (4.6.3).
Adding UseDefaultConverter is an API change, so (since picocli uses semantic versioning), this would have to go into the 4.7.0 release.

I like to add a bit more functionality before doing a 4.7.0 release, so this may take a bit more time.

Would you be open to the idea of splitting this up?
If you can take the UseDefaultConverter change out of this PR and put it into a separate PR, then that can go into the 4.7.0 release, and I can merge the remainder of this PR into master, and we can do a 4.6.3 release that includes this relatively soon.

@remkop remkop added this to the 4.6.3 milestone Dec 8, 2021
@remkop remkop modified the milestones: 4.6.3, 4.7 Jan 14, 2022
@remkop remkop force-pushed the generic_collection_args branch from d220d04 to 43a101c Compare February 10, 2022 05:23
remkop
remkop previously approved these changes Feb 10, 2022
@remkop remkop merged commit 98f2647 into remkop:main Feb 10, 2022
remkop added a commit that referenced this pull request Feb 10, 2022
remkop added a commit that referenced this pull request Mar 1, 2022
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Use generic types in containers (e.g. List, Map)
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