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Copyright © 2013 Andrey Semashev
+ Distributed under the Boost Software License, Version 1.0. (See accompanying + file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) +
+
+ BOOST_EXPLICIT_OPERATOR_BOOL()
and BOOST_CONSTEXPR_EXPLICIT_OPERATOR_BOOL()
are compatibility helper macros that expand
+ to an explicit conversion operator to bool
.
+ For compilers not supporting explicit conversion operators introduced in C++11
+ the macros expand to a conversion operator that implements the safe
+ bool idiom. In case if the compiler is not able to handle safe bool
+ idiom well the macros expand to a regular conversion operator to bool
.
+
+ Both macros are intended to be placed within a user's class definition. The
+ generated conversion operators will be implemented in terms of operator!()
+ that should be defined by user in this class. In case of BOOST_CONSTEXPR_EXPLICIT_OPERATOR_BOOL()
the generated conversion operator will be
+ declared constexpr
which requires
+ the corresponding operator!()
+ to also be constexpr
.
+
template< typename T > +class my_ptr +{ + T* m_p; + +public: + BOOST_EXPLICIT_OPERATOR_BOOL() + + bool operator!() const + { + return !m_p; + } +}; ++
+ Now my_ptr
can be used in conditional
+ expressions, similarly to a regular pointer:
+
my_ptr< int > p; +if (p) + std::cout << "true" << std::endl; ++
Last revised: November 17, 2013 at 17:08:52 GMT |
++ |