forked from boostorg/core
87 lines
2.1 KiB
Plaintext
87 lines
2.1 KiB
Plaintext
[/
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/ Copyright (c) 2013 Andrey Semashev
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/
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/ Distributed under the Boost Software License, Version 1.0. (See accompanying
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/ file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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/]
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[section:explicit_operator_bool explicit_operator_bool]
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[/=================]
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[simplesect Authors]
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[/=================]
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* Andrey Semashev
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[endsimplesect]
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[/===============]
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[section Overview]
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[/===============]
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Header `<boost/core/explicit_operator_bool.hpp>` provides
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`BOOST_EXPLICIT_OPERATOR_BOOL()`, `BOOST_EXPLICIT_OPERATOR_BOOL_NOEXCEPT()`
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and `BOOST_CONSTEXPR_EXPLICIT_OPERATOR_BOOL()` compatibility helper macros
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that expand to an explicit conversion operator to `bool`. For compilers not
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supporting explicit conversion operators introduced in C++11 the macros expand
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to a conversion operator that implements the
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[@http://en.wikibooks.org/wiki/More_C%2B%2B_Idioms/Safe_bool safe bool idiom].
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In case if the compiler is not able to handle safe bool idiom well the macros
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expand to a regular conversion operator to `bool`.
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[endsect]
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[/===============]
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[section Examples]
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[/===============]
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Both macros are intended to be placed within a user's class definition. The
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generated conversion operators will be implemented in terms of `operator!()`
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that should be defined by user in this class. In case of
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`BOOST_CONSTEXPR_EXPLICIT_OPERATOR_BOOL()` the generated conversion operator
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will be declared `constexpr` which requires the corresponding `operator!()`
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to also be `constexpr`.
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``
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template< typename T >
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class my_ptr
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{
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T* m_p;
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public:
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BOOST_EXPLICIT_OPERATOR_BOOL()
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bool operator!() const
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{
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return !m_p;
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}
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};
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``
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Now `my_ptr` can be used in conditional expressions, similarly to a regular pointer:
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``
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my_ptr< int > p;
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if (p)
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std::cout << "true" << std::endl;
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``
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[endsect]
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[/==============]
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[section History]
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[/==============]
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[heading boost 1.56]
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* Added new macros `BOOST_EXPLICIT_OPERATOR_BOOL_NOEXCEPT` and `BOOST_CONSTEXPR_EXPLICIT_OPERATOR_BOOL` to define `noexcept` and `constexpr` operators.
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* The header moved to Boost.Core.
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[heading boost 1.55]
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* The macro was extracted from Boost.Log.
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[endsect]
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[endsect]
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