projects / ceph.git / blame
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1 | [/ |
| 2 | / Copyright (c) 2013 Andrey Semashev | |
| 3 | / | |
| 4 | / Distributed under the Boost Software License, Version 1.0. (See accompanying | |
| 5 | / file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) | |
| 6 | /] | |
| 7 | ||
| 8 | [section:explicit_operator_bool explicit_operator_bool] | |
| 9 | ||
| 10 | [/=================] | |
| 11 | [simplesect Authors] | |
| 12 | [/=================] | |
| 13 | ||
| 14 | * Andrey Semashev | |
| 15 | ||
| 16 | [endsimplesect] | |
| 17 | ||
| 18 | [/===============] | |
| 19 | [section Overview] | |
| 20 | [/===============] | |
| 21 | ||
| 22 | Header `<boost/core/explicit_operator_bool.hpp>` provides | |
| 23 | `BOOST_EXPLICIT_OPERATOR_BOOL()`, `BOOST_EXPLICIT_OPERATOR_BOOL_NOEXCEPT()` | |
| 24 | and `BOOST_CONSTEXPR_EXPLICIT_OPERATOR_BOOL()` compatibility helper macros | |
| 25 | that expand to an explicit conversion operator to `bool`. For compilers not | |
| 26 | supporting explicit conversion operators introduced in C++11 the macros expand | |
| 27 | to a conversion operator that implements the | |
| 28 | [@http://en.wikibooks.org/wiki/More_C%2B%2B_Idioms/Safe_bool safe bool idiom]. | |
| 29 | In case if the compiler is not able to handle safe bool idiom well the macros | |
| 30 | expand to a regular conversion operator to `bool`. | |
| 31 | ||
| 32 | [endsect] | |
| 33 | ||
| 34 | [/===============] | |
| 35 | [section Examples] | |
| 36 | [/===============] | |
| 37 | ||
| 38 | Both macros are intended to be placed within a user's class definition. The | |
| 39 | generated conversion operators will be implemented in terms of `operator!()` | |
| 40 | that should be defined by user in this class. In case of | |
| 41 | `BOOST_CONSTEXPR_EXPLICIT_OPERATOR_BOOL()` the generated conversion operator | |
| 42 | will be declared `constexpr` which requires the corresponding `operator!()` | |
| 43 | to also be `constexpr`. | |
| 44 | ||
| 45 | `` | |
| 46 | template< typename T > | |
| 47 | class my_ptr | |
| 48 | { | |
| 49 | T* m_p; | |
| 50 | ||
| 51 | public: | |
| 52 | BOOST_EXPLICIT_OPERATOR_BOOL() | |
| 53 | ||
| 54 | bool operator!() const | |
| 55 | { | |
| 56 | return !m_p; | |
| 57 | } | |
| 58 | }; | |
| 59 | `` | |
| 60 | ||
| 61 | Now `my_ptr` can be used in conditional expressions, similarly to a regular pointer: | |
| 62 | ||
| 63 | `` | |
| 64 | my_ptr< int > p; | |
| 65 | if (p) | |
| 66 | std::cout << "true" << std::endl; | |
| 67 | `` | |
| 68 | ||
| 69 | [endsect] | |
| 70 | ||
| 71 | [/==============] | |
| 72 | [section History] | |
| 73 | [/==============] | |
| 74 | ||
| 75 | [heading boost 1.56] | |
| 76 | ||
| 77 | * Added new macros `BOOST_EXPLICIT_OPERATOR_BOOL_NOEXCEPT` and `BOOST_CONSTEXPR_EXPLICIT_OPERATOR_BOOL` to define `noexcept` and `constexpr` operators. | |
| 78 | * The header moved to Boost.Core. | |
| 79 | ||
| 80 | [heading boost 1.55] | |
| 81 | ||
| 82 | * The macro was extracted from Boost.Log. | |
| 83 | ||
| 84 | [endsect] | |
| 85 | ||
| 86 | [endsect] |