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https://issues.apache.org/jira/browse/BEAM-2261?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17546479#comment-17546479
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Kenneth Knowles commented on BEAM-2261:
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This issue has been migrated to https://github.com/apache/beam/issues/18347
> Add the ability to override values set with @Default.YYY on PipelineOptions
> ---------------------------------------------------------------------------
>
> Key: BEAM-2261
> URL: https://issues.apache.org/jira/browse/BEAM-2261
> Project: Beam
> Issue Type: Improvement
> Components: sdk-java-core
> Reporter: Luke Cwik
> Priority: P3
> Labels: Clarified
>
> Users may want to set a value only if the value isn't the default.
> When a user calls *PipelineOptionsFactory.fromArgs(args).as(Options.class)*
> they cannot tell if a user set the value from the command-line or whether the
> value is a default that was generated through the usage of the *@Default.YYY*
> annotations.
> There is currently no method to introspect whether a default is set and we
> could:
> * add a *isOptionSet()* method, but this adds many methods to the interfaces
> * ask whether something is the default or set by name or by method reference,
> *options.isSet("options" / method)*, but is brittle to any name changes in
> options.
> * allowing users to override with another interface defining a new
> *@Default.YYY* is difficult because:
> ** multiple inheritance makes choosing a default difficult:
> {code}
> MyPipelineOptions extends OptionsA, OptionsB { }
> OptionsA {
> @Default.String("A")
> String getString();
> }
> OptionsB {
> @Default.String("B")
> String getString();
> }
> {code}
> ** even if the was little ambiguity initially with MyPipelineOptions defined
> as:
> {code}
> MyPipelineOptions extends OptionsA, OptionsB {
> @Default.String("C")
> String getString();
> }
> {code}
> defaults are resolved lazily on first access and it would be strange if the
> default resolved depending on the order of "as" calls.
> {code}
> options.as(MyPipelineOptions.class).getString()
> options.as(OptionsA.class).getString()
> options.as(OptionsB.class).getString()
> would all provide different answers.
> {code}
> Finally that leaves us with an option to add support for merging
> PipelineOptions (as long as they are compatible).
> {code}
> PipelineOptions PipelineOptionsFactory.merge(PipelineOptions ... options)
> {code}
> where all subsequent options overwrite any prior set options and the empty
> array returning the default *PipelineOptionsFactory.create()*
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