Package org.apache.flink.table.annotation

Annotation Type FunctionHint

  • @PublicEvolving
@Retention(RUNTIME)
@Target({TYPE,METHOD})
@Repeatable(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 Description
      DataTypeHint accumulator
      Explicitly defines the intermediate result type that a function uses as accumulator.
      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

        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

        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

        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:
        {""}

      • accumulator

        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

        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