Tony Xu created LUCENE-9395:
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Summary: ConstantValuesSource creates DoubleValues unnecessarily
Key: LUCENE-9395
URL: https://issues.apache.org/jira/browse/LUCENE-9395
Project: Lucene - Core
Issue Type: Improvement
Components: core/search
Affects Versions: 8.5.2
Reporter: Tony Xu
At my work we use ConstantValuesSource to represent default values or a
constant query-level feature by calling `DoubleValuesSource.constant`. I
realized under the hood the `ConstantValuesSource.getDoubleValues` creates a
new `DoubleValues` which simply return the specified value each time it is
called.
Unless I missed something, I don't see risk of creating one `DoubleValues` as
use it as the return value of all getDoubleValues() calls given that the
`DoubleValues` doesn't maintain any state.
We can also offer the user flexibilities of how to initialize it.
1) `DoubleValuesSource.constant(double constant)` – we can eagerly initialize
an `DoubleValues` that returns the constant and make it the return value of all
getDoubleValues() calls.
2) `DoubleValuesSource.constant(DoubleSupplier supplier)` – For lazy
evaluation if the constant takes some time to compute and user expects the
returned DVS will not be used in all code path.
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