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third_party/eigen/test/MovableScalar.h

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+// This file is part of Eigen, a lightweight C++ template library
+// for linear algebra.
+//
+// Copyright (C) 2020 Sebastien Boisvert <seb@boisvert.info>
+//
+// This Source Code Form is subject to the terms of the Mozilla
+// Public License v. 2.0. If a copy of the MPL was not distributed
+// with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#ifndef EIGEN_MISC_MOVABLE_SCALAR_H
+#define EIGEN_MISC_MOVABLE_SCALAR_H
+
+namespace Eigen {
+template <typename Scalar>
+struct MovableScalar {
+  MovableScalar() : m_data(new Scalar) {}
+  ~MovableScalar() { delete m_data; }
+  MovableScalar(const MovableScalar& other) : m_data(new Scalar) { set(other.get()); }
+  MovableScalar(MovableScalar&& other) noexcept : m_data(other.m_data) { other.m_data = nullptr; }
+  MovableScalar& operator=(const MovableScalar& other) {
+    set(other.get());
+    return *this;
+  }
+  MovableScalar& operator=(MovableScalar&& other) noexcept {
+    m_data = other.m_data;
+    other.m_data = nullptr;
+    return *this;
+  }
+  MovableScalar(const Scalar& scalar) : m_data(new Scalar) { set(scalar); }
+
+  operator Scalar() const { return get(); }
+
+ private:
+  void set(const Scalar& value) {
+    eigen_assert(m_data != nullptr);
+    // suppress compiler warnings
+    if (m_data != nullptr) *m_data = value;
+  }
+  Scalar get() const {
+    eigen_assert(m_data != nullptr);
+    // suppress compiler warnings
+    return m_data == nullptr ? Scalar() : *m_data;
+  }
+  Scalar* m_data = nullptr;
+};
+
+template <typename Scalar>
+struct NumTraits<MovableScalar<Scalar>> : NumTraits<Scalar> {
+  enum { RequireInitialization = 1 };
+};
+
+}  // namespace Eigen
+
+#endif