aljoscha opened a new pull request #12412:
URL: https://github.com/apache/flink/pull/12412
## What is the purpose of the change
From the Jira issue:
Currently, we have an interface `WatermarkStrategy`, which is a
`TimestampAssignerSupplier` and `WatermarkGeneratorSupplier`. The very first
design (which is also currently implemented) also added `WatermarkStrategies`
as a convenience builder for a `WatermarkStrategy`. However, I don't think
users will ever implement a `WatermarkStrategy` but always wrap it in a
builder. I also think that `WatermarkStrategy` itself is already that builder
and we currently have two levels of builders, which also makes them harder to
use in the `DataStream API` because of type checking issues.
I'm proposing to remove `WatermarkStrategies` and to instead put the static
methods directly into `WatermarkStrategy` and also to remove the `build()`
method. Instead of a `build()` method, API methods on `WatermarkStrategy` just
keep "piling" features on top of a base `WatermarkStrategy` via wrapping.
Example to show what I mean for the API (current):
```
DataStream<MyType> input = ...;
input.assignTimestampsAndWatermarks(
WatermarkStrategies.<MyType>.forMonotonousTimestamps().build());
```
with this change:
```
DataStream<MyType> input = ...;
input.assignTimestampsAndWatermarks(
WatermarkStrategy.forMonotonousTimestamps());
```
## Brief change log
- remove `WatermarkStrategies` and instead move all code to
`WatermarkStrategy`
## Verifying this change
- covered by existing tests
- new tests are added to verify how `WatermarkStrategy` can be used on
`DataStream.assignTimestampsAndWatermarks()`
## Does this pull request potentially affect one of the following parts:
- The public API, i.e., is any changed class annotated with
`@Public(Evolving)`: *yes*
## Documentation
I didn't yet change the documentation. I would update that once we agree on
the change.
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