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| 1 | //===-- include/flang/Common/reference.h ------------------------*- C++ -*-===// |
|---|---|
| 2 | // |
| 3 | // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| 4 | // See https://llvm.org/LICENSE.txt for license information. |
| 5 | // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| 6 | // |
| 7 | //===----------------------------------------------------------------------===// |
| 8 | |
| 9 | // Implements a better std::reference_wrapper<> template class with |
| 10 | // move semantics, equality testing, and member access. |
| 11 | // Use Reference<A> in place of a real A& reference when assignability is |
| 12 | // required; safer than a bare pointer because it's guaranteed to not be null. |
| 13 | |
| 14 | #ifndef FORTRAN_COMMON_REFERENCE_H_ |
| 15 | #define FORTRAN_COMMON_REFERENCE_H_ |
| 16 | #include <type_traits> |
| 17 | namespace Fortran::common { |
| 18 | template <typename A> class Reference { |
| 19 | public: |
| 20 | using type = A; |
| 21 | Reference(type &x) : p_{&x} {} |
| 22 | Reference(const Reference &that) : p_{that.p_} {} |
| 23 | Reference(Reference &&that) : p_{that.p_} {} |
| 24 | Reference &operator=(const Reference &that) { |
| 25 | p_ = that.p_; |
| 26 | return *this; |
| 27 | } |
| 28 | Reference &operator=(Reference &&that) { |
| 29 | p_ = that.p_; |
| 30 | return *this; |
| 31 | } |
| 32 | |
| 33 | // Implicit conversions to references are supported only for |
| 34 | // const-qualified types in order to avoid any pernicious |
| 35 | // creation of a temporary copy in cases like: |
| 36 | // Reference<type> ref; |
| 37 | // const Type &x{ref}; // creates ref to temp copy! |
| 38 | operator std::conditional_t<std::is_const_v<type>, type &, void>() |
| 39 | const noexcept { |
| 40 | if constexpr (std::is_const_v<type>) { |
| 41 | return *p_; |
| 42 | } |
| 43 | } |
| 44 | |
| 45 | type &get() const noexcept { return *p_; } |
| 46 | type *operator->() const { return p_; } |
| 47 | type &operator*() const { return *p_; } |
| 48 | |
| 49 | bool operator==(std::add_const_t<A> &that) const { |
| 50 | return p_ == &that || *p_ == that; |
| 51 | } |
| 52 | bool operator!=(std::add_const_t<A> &that) const { return !(*this == that); } |
| 53 | bool operator==(const Reference &that) const { |
| 54 | return p_ == that.p_ || *this == *that.p_; |
| 55 | } |
| 56 | bool operator!=(const Reference &that) const { return !(*this == that); } |
| 57 | |
| 58 | private: |
| 59 | type *p_; // never null |
| 60 | }; |
| 61 | template <typename A> Reference(A &) -> Reference<A>; |
| 62 | } // namespace Fortran::common |
| 63 | #endif |
| 64 |
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