SpecializedFunction (Flink : Table : Common 2.1.0 API)

All Superinterfaces:

FunctionDefinition

All Known Implementing Classes:

BuiltInFunctionDefinition
```
@PublicEvolving
public interface SpecializedFunction
extends FunctionDefinition
```
A FunctionDefinition that can provide a runtime implementation (i.e. the function's body) that is specialized for the given call and session.
The planner tries to defer the specialization until shortly before code generation, where the information given by a FunctionDefinition is not enough anymore and a subclass of UserDefinedFunction is required for runtime.
This interface is useful when the runtime code should know about information that is only available after planning (e.g. local session time zone or precision/scale of decimal return type).
A UserDefinedFunction that is registered in the API is implicitly specialized but can also implement this interface to reconfigure itself before runtime.
Note: This interface is a rather low level kind of function but useful for advanced users.

Nested Class Summary

Nested Classes
Modifier and Type	Interface	Description
`static interface`	`SpecializedFunction.ExpressionEvaluator`	Serializable factory that can be passed into a `UserDefinedFunction` for evaluating previously defined expression during runtime.
`static interface`	`SpecializedFunction.ExpressionEvaluatorFactory`	Helper interface for creating `SpecializedFunction.ExpressionEvaluator`s.
`static interface`	`SpecializedFunction.SpecializedContext`	Provides call and session information for the specialized function.

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method	Description
`UserDefinedFunction`	`specialize(SpecializedFunction.SpecializedContext context)`	Provides a runtime implementation that is specialized for the given call and session.

Methods inherited from interface org.apache.flink.table.functions.FunctionDefinition
getKind, getRequirements, getTypeInference, isDeterministic, supportsConstantFolding

- Method Detail
  - specialize
```
UserDefinedFunction specialize(SpecializedFunction.SpecializedContext context)
```
    Provides a runtime implementation that is specialized for the given call and session.
    The method must return an instance of UserDefinedFunction or throw a TableException if the given call is not supported. The returned instance must have the same FunctionDefinition semantics but can have a different FunctionDefinition.getTypeInference(DataTypeFactory) implementation.