include/paimon/string_builder.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. template <typename T>

// Adapted from Apache Arrow
// https://github.com/apache/arrow/blob/apache-arrow-17.0.0/cpp/src/arrow/util/string_builder.h

#pragma once

#include <memory>
#include <ostream>
#include <sstream>
#include <string>
#include <utility>

#include "paimon/visibility.h"

namespace paimon::util {

namespace detail {

class PAIMON_EXPORT StringStreamWrapper {
 public:
    StringStreamWrapper() : sstream_(std::make_unique<std::ostringstream>()), ostream_(*sstream_) {}
    ~StringStreamWrapper() = default;

    std::ostream& stream() {
        return ostream_;
    }
    std::string str() {
        return sstream_->str();
    }

 protected:
    std::unique_ptr<std::ostringstream> sstream_;
    std::ostream& ostream_;
};

}  // namespace detail

template <typename Head>
void StringBuilderRecursive(std::ostream& stream, Head&& head) {
    stream << head;
}

template <typename Head, typename... Tail>
void StringBuilderRecursive(std::ostream& stream, Head&& head, Tail&&... tail) {
    StringBuilderRecursive(stream, std::forward<Head>(head));
    StringBuilderRecursive(stream, std::forward<Tail>(tail)...);
}

template <typename... Args>
std::string StringBuilder(Args&&... args) {
    detail::StringStreamWrapper ss;
    StringBuilderRecursive(ss.stream(), std::forward<Args>(args)...);
    return ss.str();
}

/// CRTP helper for declaring string representation. Defines operator<<
template <typename T>
class PAIMON_EXPORT ToStringOstreamable {
 public:
    ~ToStringOstreamable() {
        static_assert(std::is_same_v<decltype(std::declval<const T>().ToString()), std::string>,
                      "ToStringOstreamable depends on the method T::ToString() const");
    }

 private:
    const T& cast() const {
        return static_cast<const T&>(*this);
    }

    friend inline std::ostream& operator<<(std::ostream& os, const ToStringOstreamable& t) {
        return os << t.cast().ToString();
    }
};

}  // namespace paimon::util