org.apache.flink.table.types.inference

Class TypeInferenceUtil

java.lang.Object

org.apache.flink.table.types.inference.TypeInferenceUtil

@Internal
public final class TypeInferenceUtil
extends Object

Utility for performing type inference.

The following steps summarize the envisioned type inference process. Not all features are implemented or exposed through the API yet (*).

• 1. Validate number of arguments.
• 2. (*) Apply assignment operators on the call by permuting operands and adding default values. These are preparations for CallContext.
• 3. For resolving unknown (NULL) operands: Access the outer wrapping call and try to get its operand type for the return type of the actual call. E.g. for takes_string(this_function(NULL)) infer operands from takes_string(NULL) and use the inferred string type as the return type of this_function(NULL).
• 4. Try infer unknown operands, fail if not possible.
• 5. (*) Check the usage of DEFAULT operands are correct using validator.isOptional().
• 6. Perform input type validation.
• 7. (Optional) Infer accumulator type.
• 8. Infer return type.
• 9. (*) In the planner: Call the strategies again at any point in time to enrich a DataType that has been created from a logical type with a conversion class.
• 10. (*) In the planner: Check for an implementation evaluation method matching the operands. The matching happens class-based. Thus, for example, eval(Object) is valid for (INT). Or eval(Object...) is valid for (INT, STRING). We rely on the conversion classes specified by DataType.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	TypeInferenceUtil.Result The result of a type inference run.
static class	TypeInferenceUtil.SurroundingInfo Information what the outer world (i.e.

Method Summary

Modifier and Type	Method and Description
static String	generateSignature(String name, FunctionDefinition definition, TypeInference typeInference) Generates a signature of the given FunctionDefinition.
static TypeInferenceUtil.Result	runTypeInference(TypeInference typeInference, CallContext callContext, TypeInferenceUtil.SurroundingInfo surroundingInfo) Runs the type inference process.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

generateSignature

public static String generateSignature(String name,
                                       FunctionDefinition definition,
                                       TypeInference typeInference)

Generates a signature of the given FunctionDefinition.

runTypeInference

public static TypeInferenceUtil.Result runTypeInference(TypeInference typeInference,
                                                        CallContext callContext,
                                                        @Nullable
                                                        TypeInferenceUtil.SurroundingInfo surroundingInfo)

Runs the type inference process.

Parameters:

typeInference - type inference of the current call

callContext - call context of the current call

surroundingInfo - information about the outer wrapping call of a current function call for performing input type inference