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_SUPPORT_CPP_EXPECTED_H
  10 #define LLVM_LIBC_SUPPORT_CPP_EXPECTED_H
  11
  12 namespace __llvm_libc::cpp {
  13
  14 // This is used to hold an unexpected value so that a different constructor is
  15 // selected.
  16 template <class T> class unexpected {
  17   T value;
  18
  19 public:
  20   constexpr explicit unexpected(T value) : value(value) {}
  21   constexpr T error() { return value; }
  22 };
  23
  24 template <class T, class E> class expected {
  25   union {
  26     T exp;
  27     E unexp;
  28   };
  29   bool is_expected;
  30
  31 public:
  32   constexpr expected(T exp) : exp(exp), is_expected(true) {}
  33   constexpr expected(unexpected<E> unexp)
  34       : unexp(unexp.error()), is_expected(false) {}
  35
  36   constexpr bool has_value() { return is_expected; }
  37
  38   constexpr T value() { return exp; }
  39   constexpr E error() { return unexp; }
  40
  41   constexpr operator T() { return exp; }
  42   constexpr operator bool() { return is_expected; }
  43
  44   constexpr T &operator*() { return exp; }
  45   constexpr const T &operator*() const { return exp; }
  46   constexpr T *operator->() { return &exp; }
  47   constexpr const T *operator->() const { return &exp; }
  48 };
  49
  50 } // namespace __llvm_libc::cpp
  51
  52 #endif // LLVM_LIBC_SUPPORT_CPP_EXPECTED_H