Luke Cwik created BEAM-2261:
-------------------------------
Summary: 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: Minor
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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