```
@PublicEvolving
@Retention(RUNTIME)
@Target({TYPE,METHOD})
@Repeatable(FunctionHints.class)
public @interface FunctionHint
```
A hint that influences the reflection-based extraction of arguments, accumulator, and output 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,
 // the arguments have names and are optional
```
See Also:

DataTypeHint, ArgumentHint

Optional Element Summary

Optional Elements
Modifier and Type	Optional Element	Description
`DataTypeHint`	`accumulator`	Explicitly defines the intermediate result type (i.e. state entry) that an aggregating function uses as its accumulator.
`ArgumentHint[]`	`argument`	Deprecated. Use `arguments()` instead.
`String[]`	`argumentNames`	Deprecated. Use `arguments()` instead.
`ArgumentHint[]`	`arguments`	Explicitly lists the arguments 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.
`StateHint[]`	`state`	Explicitly lists the intermediate results (i.e. state entries) of a function that is managed by the framework (i.e.

- Element Detail
  - input
```
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() needs to be specified manually if required.
    Use arguments() for more control about argument names and argument kinds.
    
    Default:
    
    {@org.apache.flink.table.annotation.DataTypeHint}
- - isVarArgs
```
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
- - arguments
```
ArgumentHint[] arguments
```
    Explicitly lists the arguments that a function takes as input. Including their names, data types, kinds, and whether they are optional.
    It is recommended to use this parameter instead of input(). Using both input() and this parameter is not allowed. Specifying the list of arguments manually disables the entire reflection-based extraction around arguments.
    
    Default:
    
    {}
- - accumulator
```
DataTypeHint accumulator
```
    Explicitly defines the intermediate result type (i.e. state entry) that an aggregating function uses as its accumulator. The entry is managed by the framework (usually via Flink's managed state).
    By default, an explicit accumulator type is undefined and the reflection-based extraction is used.
    This parameter is primarily intended for aggregating functions (i.e. AggregateFunction and TableAggregateFunction). It is recommended to use state() for ProcessTableFunction.
    
    Default:
    
    @org.apache.flink.table.annotation.DataTypeHint
- - state
```
StateHint[] state
```
    Explicitly lists the intermediate results (i.e. state entries) of a function that is managed by the framework (i.e. Flink managed state). Including their names and data types.
    State hints are primarily intended for ProcessTableFunction. A PTF supports multiple state entries at the beginning of an eval()/onTimer() method (after an optional context parameter).
    Aggregating functions (i.e. AggregateFunction and TableAggregateFunction) support a single state entry at the beginning of an accumulate()/retract() method (i.e. the accumulator).
    By default, explicit state is undefined and the reflection-based extraction is used where StateHint is present.
    Using both accumulator() and this parameter is not allowed. Specifying the list of state entries manually disables the entire reflection-based extraction around StateHint and accumulators for aggregating functions.
    
    Default:
    
    {}
- - output
```
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
- - argumentNames
```
@Deprecated
String[] argumentNames
```
    Deprecated.
    Use arguments() instead.
    
    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
```
@Deprecated
ArgumentHint[] argument
```
    Deprecated.
    Use arguments() instead.
    
    Explicitly lists the arguments that a function takes as input. Including their names, data types, kinds, and whether they are optional.
    It is recommended to use this parameter instead of input(). Specifying the list of arguments manually disables the entire reflection-based extraction around arguments.
    
    Default:
    
    {}

Annotation Type FunctionHint

Optional Element Summary

Element Detail

input

isVarArgs

arguments

accumulator

state

output

argumentNames

argument