be/src/vec/functions/function_fake.h

// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License.

#pragma once

#include <stddef.h>

#include <memory>

#include "common/status.h"
#include "vec/core/column_numbers.h"
#include "vec/core/types.h"
#include "vec/data_types/data_type.h"
#include "vec/data_types/data_type_number.h"
#include "vec/functions/function.h"

namespace doris {
class FunctionContext;
namespace vectorized {
class Block;
} // namespace vectorized
} // namespace doris

namespace doris::vectorized {

struct UDTFImpl {
    static DataTypePtr get_return_type_impl(const DataTypes& arguments) {
        return std::make_shared<DataTypeUInt8>(); //just fake return uint8
    }
    static std::string get_error_msg() {
        return "UDTF function do not support this, it's should execute with lateral view.";
    }
    static DataTypes get_variadic_argument_types() { return {}; }
};

// FunctionFake is use for some function call expr only work at prepare/open phase, do not support execute().
template <typename Impl>
class FunctionFake : public IFunction {
public:
    static constexpr auto name = "fake";

    static FunctionPtr create() { return std::make_shared<FunctionFake>(); }

    String get_name() const override { return name; }

    size_t get_number_of_arguments() const override { return 0; }

    bool is_variadic() const override { return true; }

    DataTypePtr get_return_type_impl(const DataTypes& arguments) const override {
        return Impl::get_return_type_impl(arguments);
    }

    DataTypes get_variadic_argument_types_impl() const override {
        return Impl::get_variadic_argument_types();
    }

    bool use_default_implementation_for_nulls() const override {
        if constexpr (std::is_same_v<Impl, UDTFImpl>) {
            return false;
        }
        return true;
    }

    bool use_default_implementation_for_constants() const override { return false; }

    Status execute_impl(FunctionContext* context, Block& block, const ColumnNumbers& arguments,
                        uint32_t result, size_t input_rows_count) const override {
        return Status::NotSupported(Impl::get_error_msg());
    }
};

} // namespace doris::vectorized