model.h

Go to the documentation of this file.

// Copyright 2010-2025 Google LLC
// 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 ORTOOLS_SAT_MODEL_H_
#define ORTOOLS_SAT_MODEL_H_
 
#include <cstddef>
#include <cstdio>
#include <ctime>
#include <functional>
#include <memory>
#include <string>
#include <vector>
 
#include "absl/container/flat_hash_map.h"
#include "absl/log/check.h"
#include "ortools/base/logging.h"
 
namespace operations_research {
namespace sat {

class Model {
  // FastTypeId<Type>() evaluates at compile/link-time to a unique integer for
  // the passed in type. Their values are neither contiguous nor small, making
  // them unfit for using as an index into a vector, but a good match for keys
  // into maps or straight up comparisons. Note that on 64-bit (unix) systems
  // size_t is 64-bit while int is 32-bit and the compiler will happily and
  // quietly assign such a 64-bit value to a 32-bit integer. While a client
  // should never do that it SHOULD still be safe, assuming the BSS segment
  // doesn't span more than 4GiB.
  template <typename Type>
  static inline size_t FastTypeId() {
    static_assert(sizeof(char*) <= sizeof(size_t),
                  "ptr size too large for size_t");
 
    // This static variable isn't actually used, only its address, so there are
    // no concurrency issues.
    static char dummy_var;
    return reinterpret_cast<size_t>(&dummy_var);
  }
 
 public:
  Model() = default;
 
  ~Model() {
    // The order of deletion seems to be platform dependent.
    // We force a reverse order on the cleanup vector.
    for (int i = cleanup_list_.size() - 1; i >= 0; --i) {
      cleanup_list_[i].reset();
    }
  }

  explicit Model(std::string name) : name_(name) {}
 
  // This type is neither copyable nor movable.
  Model(const Model&) = delete;
  Model& operator=(const Model&) = delete;

  template <typename T>
  T Add(std::function<T(Model*)> f) {
    return f(this);
  }

  template <typename T>
  T Get(std::function<T(const Model&)> f) const {
    return f(*this);
  }

  template <typename T>
  T* GetOrCreate() {
    const size_t type_id = FastTypeId<T>();
    auto find = singletons_.find(type_id);
    if (find != singletons_.end()) {
      return static_cast<T*>(find->second);
    }
 
    // New element.
    // TODO(user): directly store std::unique_ptr<> in singletons_?
    T* new_t = MyNew<T>(0);
    singletons_[type_id] = new_t;
    TakeOwnership(new_t);
    return new_t;
  }

  template <typename T>
  const T* Get() const {
    const auto& it = singletons_.find(FastTypeId<T>());
    return it != singletons_.end() ? static_cast<const T*>(it->second)
                                   : nullptr;
  }

  template <typename T>
  T* Mutable() const {
    const auto& it = singletons_.find(FastTypeId<T>());
    return it != singletons_.end() ? static_cast<T*>(it->second) : nullptr;
  }

  template <typename T>
  T* TakeOwnership(T* t) {
    cleanup_list_.emplace_back(new Delete<T>(t));
    return t;
  }

  template <typename T>
  T* Create() {
    T* new_t = MyNew<T>(0);
    TakeOwnership(new_t);
    return new_t;
  }

  template <typename T>
  void Register(T* non_owned_class) {
    const size_t type_id = FastTypeId<T>();
    CHECK(!singletons_.contains(type_id));
    singletons_[type_id] = non_owned_class;
  }
 
  const std::string& Name() const { return name_; }
 
 private:
  // We want to call the constructor T(model*) if it exists or just T() if
  // it doesn't. For this we use some template "magic":
  // - The first MyNew() will only be defined if the type in decltype() exist.
  // - The second MyNew() will always be defined, but because of the ellipsis
  //   it has lower priority that the first one.
  template <typename T>
  decltype(T(static_cast<Model*>(nullptr)))* MyNew(int) {
    return new T(this);
  }
  template <typename T>
  T* MyNew(...) {
    return new T();
  }
 
  const std::string name_;
 
  // Map of FastTypeId<T> to a "singleton" of type T.
  absl::flat_hash_map</*typeid*/ size_t, void*> singletons_;
 
  struct DeleteInterface {
    virtual ~DeleteInterface() = default;
  };
  template <typename T>
  class Delete : public DeleteInterface {
   public:
    explicit Delete(T* t) : to_delete_(t) {}
    ~Delete() override = default;
 
   private:
    std::unique_ptr<T> to_delete_;
  };
 
  // The list of items to delete.
  //
  // TODO(user): I don't think we need the two layers of unique_ptr, but we
  // don't care too much about efficiency here and this was easier to get
  // working.
  std::vector<std::unique_ptr<DeleteInterface>> cleanup_list_;
};
 
}  // namespace sat
}  // namespace operations_research
 
#endif  // ORTOOLS_SAT_MODEL_H_