libc/src/__support/CPP/expected.h

   1 //===-- Holds an expected or unexpected value -------------------*- 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 #ifndef LLVM_LIBC_SRC___SUPPORT_CPP_EXPECTED_H
  10 #define LLVM_LIBC_SRC___SUPPORT_CPP_EXPECTED_H
  11
  12 #include "src/__support/macros/attributes.h"
  13 #include "src/__support/macros/config.h"
  14
  15 namespace LIBC_NAMESPACE_DECL {
  16 namespace cpp {
  17
  18 // This is used to hold an unexpected value so that a different constructor is
  19 // selected.
  20 template <class T> class unexpected {
  21   T value;
  22
  23 public:
  24   LIBC_INLINE constexpr explicit unexpected(T value) : value(value) {}
  25   LIBC_INLINE constexpr T error() { return value; }
  26 };
  27
  28 template <class T> explicit unexpected(T) -> unexpected<T>;
  29
  30 template <class T, class E> class expected {
  31   union {
  32     T exp;
  33     E unexp;
  34   };
  35   bool is_expected;
  36
  37 public:
  38   LIBC_INLINE constexpr expected(T exp) : exp(exp), is_expected(true) {}
  39   LIBC_INLINE constexpr expected(unexpected<E> unexp)
  40       : unexp(unexp.error()), is_expected(false) {}
  41
  42   LIBC_INLINE constexpr bool has_value() const { return is_expected; }
  43
  44   LIBC_INLINE constexpr T &value() { return exp; }
  45   LIBC_INLINE constexpr E &error() { return unexp; }
  46   LIBC_INLINE constexpr const T &value() const { return exp; }
  47   LIBC_INLINE constexpr const E &error() const { return unexp; }
  48
  49   LIBC_INLINE constexpr operator bool() const { return is_expected; }
  50
  51   LIBC_INLINE constexpr T &operator*() { return exp; }
  52   LIBC_INLINE constexpr const T &operator*() const { return exp; }
  53   LIBC_INLINE constexpr T *operator->() { return &exp; }
  54   LIBC_INLINE constexpr const T *operator->() const { return &exp; }
  55 };
  56
  57 } // namespace cpp
  58 } // namespace LIBC_NAMESPACE_DECL
  59
  60 #endif // LLVM_LIBC_SRC___SUPPORT_CPP_EXPECTED_H