Source:
private static SqlOperator toOp(RelDataTypeFactory typeFactory, SqlIdentifier name, final Function function) { List<RelDataType> argTypes = new ArrayList<>(); List<SqlTypeFamily> typeFamilies = new ArrayList<>(); for (FunctionParameter o : function.getParameters()) { final RelDataType type = o.getType(typeFactory); argTypes.add(type); typeFamilies.add( Util.first(type.getSqlTypeName().getFamily(), SqlTypeFamily.ANY)); } final FamilyOperandTypeChecker typeChecker = OperandTypes.family(typeFamilies, i -> function.getParameters().get(i).isOptional(), function.isVarArgs()); final List<RelDataType> paramTypes = toSql(typeFactory, argTypes); if (function instanceof ScalarFunction) { return new SqlUserDefinedFunction(name, infer((ScalarFunction) function), InferTypes.explicit(argTypes), typeChecker, paramTypes, function.isVarArgs(), function); } else if (function instanceof AggregateFunction) { return new SqlUserDefinedAggFunction(name, infer((AggregateFunction) function), InferTypes.explicit(argTypes), typeChecker, (AggregateFunction) function, false, false, Optionality.FORBIDDEN, typeFactory); } else if (function instanceof TableMacro) { return new SqlUserDefinedTableMacro(name, ReturnTypes.CURSOR, InferTypes.explicit(argTypes), typeChecker, paramTypes, (TableMacro) function); } else if (function instanceof TableFunction) { return new SqlUserDefinedTableFunction(name, ReturnTypes.CURSOR, InferTypes.explicit(argTypes), typeChecker, paramTypes, (TableFunction) function); } else { throw new AssertionError("unknown function type " + function); } }

Target:
private static SqlOperator toOp(RelDataTypeFactory typeFactory, SqlIdentifier name, final Function function) { List<RelDataType> argTypes = new ArrayList<>(); List<SqlTypeFamily> typeFamilies = new ArrayList<>(); for (FunctionParameter o : function.getParameters()) { final RelDataType type = o.getType(typeFactory); argTypes.add(type); typeFamilies.add( Util.first(type.getSqlTypeName().getFamily(), SqlTypeFamily.ANY)); } final FamilyOperandTypeChecker typeChecker = OperandTypes.family(typeFamilies, i -> function.getParameters().get(i).isOptional(), function.isVarArgs() ? i -> function.getParameters().get(i).isVarArgs() : null); final List<RelDataType> paramTypes = toSql(typeFactory, argTypes); if (function instanceof ScalarFunction) { return new SqlUserDefinedFunction(name, infer((ScalarFunction) function), InferTypes.explicit(argTypes), typeChecker, paramTypes, function.isVarArgs(), function); } else if (function instanceof AggregateFunction) { return new SqlUserDefinedAggFunction(name, infer((AggregateFunction) function), InferTypes.explicit(argTypes), typeChecker, (AggregateFunction) function, false, false, Optionality.FORBIDDEN, typeFactory); } else if (function instanceof TableMacro) { return new SqlUserDefinedTableMacro(name, ReturnTypes.CURSOR, InferTypes.explicit(argTypes), typeChecker, paramTypes, (TableMacro) function); } else if (function instanceof TableFunction) { return new SqlUserDefinedTableFunction(name, ReturnTypes.CURSOR, InferTypes.explicit(argTypes), typeChecker, paramTypes, (TableFunction) function); } else { throw new AssertionError("unknown function type " + function); } }