org.apache.flink.table.functions.SpecializedFunction Maven / Gradle / Ivy
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*
* http://www.apache.org/licenses/LICENSE-2.0
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package org.apache.flink.table.functions;
import org.apache.flink.annotation.PublicEvolving;
import org.apache.flink.configuration.ReadableConfig;
import org.apache.flink.table.api.TableException;
import org.apache.flink.table.catalog.DataTypeFactory;
import org.apache.flink.table.types.inference.CallContext;
/**
* A {@link 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 {@link FunctionDefinition} is not enough anymore and a subclass of {@link
* 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 {@link 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.
*/
@PublicEvolving
public interface SpecializedFunction extends FunctionDefinition {
/**
* Provides a runtime implementation that is specialized for the given call and session.
*
*
The method must return an instance of {@link UserDefinedFunction} or throw a {@link
* TableException} if the given call is not supported. The returned instance must have the same
* {@link FunctionDefinition} semantics but can have a different {@link
* #getTypeInference(DataTypeFactory)} implementation.
*/
UserDefinedFunction specialize(SpecializedContext context);
/** Provides call and session information for the specialized function. */
interface SpecializedContext {
/** Returns the context of the current call. */
CallContext getCallContext();
/** Gives read-only access to the configuration of the current session. */
ReadableConfig getConfiguration();
/** Returns the classloader used to resolve built-in functions. */
ClassLoader getBuiltInClassLoader();
}
}