ceph/src/boost/libs/leaf/examples/print_half.cpp

   1 // Copyright (c) 2018-2020 Emil Dotchevski and Reverge Studios, Inc.
   2
   3 // Distributed under the Boost Software License, Version 1.0. (See accompanying
   4 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   5
   6 // This program is an adaptation of the following Boost Outcome example:
   7 // https://github.com/ned14/outcome/blob/master/doc/src/snippets/using_result.cpp
   8
   9 #include <boost/leaf/handle_errors.hpp>
  10 #include <boost/leaf/pred.hpp>
  11 #include <boost/leaf/result.hpp>
  12 #include <algorithm>
  13 #include <ctype.h>
  14 #include <string>
  15 #include <iostream>
  16
  17 namespace leaf = boost::leaf;
  18
  19 enum class ConversionErrc
  20 {
  21     EmptyString = 1,
  22     IllegalChar,
  23     TooLong
  24 };
  25
  26 leaf::result<int> convert(const std::string& str) noexcept
  27 {
  28     if (str.empty())
  29         return leaf::new_error(ConversionErrc::EmptyString);
  30
  31     if (!std::all_of(str.begin(), str.end(), ::isdigit))
  32         return leaf::new_error(ConversionErrc::IllegalChar);
  33
  34     if (str.length() > 9)
  35         return leaf::new_error(ConversionErrc::TooLong);
  36
  37     return atoi(str.c_str());
  38 }
  39
  40 // Do not static_store BigInt to actually work -- it's a stub.
  41 struct BigInt
  42 {
  43     static leaf::result<BigInt> fromString(const std::string& s) { return BigInt{s}; }
  44     explicit BigInt(const std::string&) { }
  45     BigInt half() const { return BigInt{""}; }
  46     friend std::ostream& operator<<(std::ostream& o, const BigInt&) { return o << "big int half"; }
  47 };
  48
  49 // This function handles ConversionErrc::TooLong errors, forwards any other error to the caller.
  50 leaf::result<void> print_half(const std::string& text)
  51 {
  52     return leaf::try_handle_some(
  53         [&]() -> leaf::result<void>
  54         {
  55             BOOST_LEAF_AUTO(r,convert(text));
  56             std::cout << r / 2 << std::endl;
  57             return { };
  58         },
  59         [&]( leaf::match<ConversionErrc, ConversionErrc::TooLong> ) -> leaf::result<void>
  60         {
  61             BOOST_LEAF_AUTO(i, BigInt::fromString(text));
  62             std::cout << i.half() << std::endl;
  63             return { };
  64         } );
  65 }
  66
  67 int main( int argc, char const * argv[] )
  68 {
  69     return leaf::try_handle_all(
  70         [&]() -> leaf::result<int>
  71         {
  72             BOOST_LEAF_CHECK( print_half(argc<2 ? "" : argv[1]) );
  73             std::cout << "ok" << std::endl;
  74             return 0;
  75         },
  76
  77         []( leaf::match<ConversionErrc, ConversionErrc::EmptyString> )
  78         {
  79             std::cerr << "Empty string!" << std::endl;
  80             return 1;
  81         },
  82
  83         []( leaf::match<ConversionErrc, ConversionErrc::IllegalChar> )
  84         {
  85             std::cerr << "Illegal char!" << std::endl;
  86             return 2;
  87         },
  88
  89         []( leaf::error_info const & unmatched )
  90         {
  91             // This will never execute in this program, but it would detect logic errors where an unknown error reaches main.
  92             // In this case, we print diagnostic information.
  93             std::cerr <<
  94                 "Unknown failure detected" << std::endl <<
  95                 "Cryptic diagnostic information follows" << std::endl <<
  96                 unmatched;
  97             return 3;
  98         } );
  99 }
 100
 101 ////////////////////////////////////////
 102
 103 #ifdef BOOST_LEAF_NO_EXCEPTIONS
 104
 105 namespace boost
 106 {
 107     BOOST_LEAF_NORETURN void throw_exception( std::exception const & e )
 108     {
 109         std::cerr << "Terminating due to a C++ exception under BOOST_LEAF_NO_EXCEPTIONS: " << e.what();
 110         std::terminate();
 111     }
 112
 113     struct source_location;
 114     BOOST_LEAF_NORETURN void throw_exception( std::exception const & e, boost::source_location const & )
 115     {
 116         throw_exception(e);
 117     }
 118 }
 119
 120 #endif