llvm/flang/lib/parser/indirection.h

// Copyright (c) 2018, NVIDIA CORPORATION.  All rights reserved.
//
// Licensed 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.

#ifndef FORTRAN_PARSER_INDIRECTION_H_
#define FORTRAN_PARSER_INDIRECTION_H_

// Defines a smart pointer template class that's rather like std::unique_ptr<>
// but further restricted, like a C++ reference, to be non-null when constructed
// or assigned.  Users need not check whether these pointers are null.
// Intended to be as invisible as possible.

#include "idioms.h"
#include <utility>

namespace Fortran::parser {

template<typename A> class Indirection {
public:
  using element_type = A;
  Indirection() = delete;
  Indirection(A *&&p) : p_{p} {
    CHECK(p_ && "assigning null pointer to Indirection");
    p = nullptr;
  }
  Indirection(A &&p) : p_{new A(std::move(p))} {}
  template<typename... ARGS>
  Indirection(ARGS &&... args) : p_{new A(std::forward<ARGS>(args)...)} {}
  Indirection(Indirection &&that) {
    CHECK(that.p_ && "constructing Indirection from null Indirection");
    p_ = that.p_;
    that.p_ = nullptr;
  }
  ~Indirection() {
    delete p_;
    p_ = nullptr;
  }
  Indirection &operator=(Indirection &&that) {
    CHECK(that.p_ && "assigning null Indirection to Indirection");
    auto tmp = p_;
    p_ = that.p_;
    that.p_ = tmp;
    return *this;
  }
  A &operator*() const { return *p_; }
  A *operator->() { return p_; }
  const A *operator->() const { return p_; }

private:
  A *p_{nullptr};
};

}  // namespace Fortran::parser
#endif  // FORTRAN_PARSER_INDIRECTION_H_