org.apache.flink.table.annotation

Annotation Type FunctionHint

@PublicEvolving
 @Retention(value=RUNTIME)
 @Target(value={TYPE,METHOD})
 @Repeatable(value=FunctionHints.class)
public @interface FunctionHint

A hint that influences the reflection-based extraction of input types, accumulator types, and output types for constructing the TypeInference logic of a UserDefinedFunction.

One or more annotations can be declared on top of a UserDefinedFunction class or individually for each eval()/accumulate() method for overloading function signatures. All hint parameters are optional. If a parameter is not defined, the default reflection-based extraction is used. Hint parameters defined on top of a UserDefinedFunction class are inherited by all eval()/accumulate() methods.

The following examples show how to explicitly specify function signatures as a whole or in part and let the default extraction do the rest:

{@code
 // accepts (INT, STRING) and returns BOOLEAN

See Also:

DataTypeHint

Optional Element Summary

Optional Elements

Modifier and Type	Optional Element and Description
DataTypeHint	accumulator Explicitly defines the intermediate result type that a function uses as accumulator.
ArgumentHint[]	argument Explicitly lists the argument that a function takes as input, including their names, types, and whether they are optional.
String[]	argumentNames Explicitly lists the argument names that a function takes as input.
DataTypeHint[]	input Explicitly lists the argument types that a function takes as input.
boolean	isVarArgs Defines that the last argument type defined in input() should be treated as a variable-length argument.
DataTypeHint	output Explicitly defines the result type that a function uses as output.

Element Detail

input

public abstract DataTypeHint[] input

Explicitly lists the argument types that a function takes as input.

By default, explicit input types are undefined and the reflection-based extraction is used.

Note: Specifying the input arguments manually disables the entire reflection-based extraction around arguments. This means that also isVarArgs() and argumentNames() need to be specified manually if required.

Default:

@org.apache.flink.table.annotation.DataTypeHint

isVarArgs

public abstract boolean isVarArgs

Defines that the last argument type defined in input() should be treated as a variable-length argument.

By default, if input() is defined, the last argument type is not a var-arg. If input() is not defined, the reflection-based extraction is used to decide about the var-arg flag, thus, this parameter is ignored.

Default:

false

argumentNames

public abstract String[] argumentNames

Explicitly lists the argument names that a function takes as input.

By default, if input() is defined, explicit argument names are undefined and this parameter can be used to provide argument names. If input() is not defined, the reflection-based extraction is used, thus, this parameter is ignored.

Default:

""

argument

public abstract ArgumentHint[] argument

Explicitly lists the argument that a function takes as input, including their names, types, and whether they are optional.

By default, it is recommended to use this parameter instead of input(). If the type of argumentHint is not defined, it will be considered an invalid argument and an exception will be thrown. Additionally, both this parameter and input() cannot be defined at the same time. If neither argument nor input() are defined, reflection-based extraction will be used.

Default:

{}

accumulator

public abstract DataTypeHint accumulator

Explicitly defines the intermediate result type that a function uses as accumulator.

By default, an explicit accumulator type is undefined and the reflection-based extraction is used.

Default:

@org.apache.flink.table.annotation.DataTypeHint

output

public abstract DataTypeHint output

Explicitly defines the result type that a function uses as output.

By default, an explicit output type is undefined and the reflection-based extraction is used.

Default:

@org.apache.flink.table.annotation.DataTypeHint