org.apache.flink.table.functions.FunctionDefinition Maven / Gradle / Ivy
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*
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*
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package org.apache.flink.table.functions;
import org.apache.flink.annotation.PublicEvolving;
import org.apache.flink.table.catalog.DataTypeFactory;
import org.apache.flink.table.types.inference.TypeInference;
import java.util.Collections;
import java.util.Set;
/**
* Definition of a function. Instances of this class provide all details necessary to validate a
* function call and perform planning.
*
* A pure function definition must not contain a runtime implementation. This can be provided by
* the planner at later stages.
*
* @see UserDefinedFunction
*/
@PublicEvolving
public interface FunctionDefinition {
/** Returns the kind of function this definition describes. */
FunctionKind getKind();
/**
* Returns the logic for performing type inference of a call to this function definition.
*
*
The type inference process is responsible for inferring unknown types of input arguments,
* validating input arguments, and producing result types. The type inference process happens
* independent of a function body. The output of the type inference is used to search for a
* corresponding runtime implementation.
*
*
Instances of type inference can be created by using {@link TypeInference#newBuilder()}.
*
*
See {@link BuiltInFunctionDefinitions} for concrete usage examples.
*/
TypeInference getTypeInference(DataTypeFactory typeFactory);
/** Returns the set of requirements this definition demands. */
default Set getRequirements() {
return Collections.emptySet();
}
/**
* Returns information about the determinism of the function's results.
*
* It returns true if and only if a call to this function is guaranteed to
* always return the same result given the same parameters. true is assumed by
* default. If the function is not purely functional like random(), date(), now(), ...
* this method must return false.
*
*
Furthermore, return false if the planner should always execute this function
* on the cluster side. In other words: the planner should not perform constant expression
* reduction during planning for constant calls to this function.
*/
default boolean isDeterministic() {
return true;
}
}