Boost
C++ Libraries
...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
Boost
C++ Libraries
...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
boost::signals2::signal_type — Specify a the template type parameters of a boost::signals2::signal using named parameters.
// In header: <boost/signals2/signal_type.hpp> template<typename A0, typename A1 = boost::parameter::void_, typename A2 = boost::parameter::void_, typename A3 = boost::parameter::void_, typename A4 = boost::parameter::void_, typename A5 = boost::parameter::void_, typename A6 = boost::parameter::void_> class signal_type { public: // types typedef implementation-detail signature_type; typedef implementation-detail combiner_type; typedef implementation-detail group_type; typedef implementation-detail group_compare_type; typedef implementation-detail slot_function_type; typedef implementation-detail extended_slot_function_type; typedef implementation-detail mutex_type; typedef typename signal<signature_type, combiner_type, ..., mutex_type> type; };
The signal_type metafunction employs the Boost.Parameter library to
allow users to specify the template type parameters of a signals2::signal
using named parameters. The resulting signal type is provided through the
signal_type::type typedef. Named template type parameters
can enhance readability of code, and provide convenience for specifying classes
which have a large number of template parameters.
The template type parameters may be passed positionally, similarly to passing them
to the signals2::signal class directly. Or, they may be passed as named template parameters
by wrapping them in one of the template keyword classes provided in the
boost::signals2::keywords namespace. The supported template keywords are:
keywords::signature_type, keywords::combiner_type,
keywords::group_type, keywords::group_compare_type,
keywords::slot_function_type, keywords::extended_slot_function_type,
and keywords::mutex_type.
The default types for unspecified template type parameters are the same as those for the signal class.
Named template type parameters are especially convenient when you only wish to change a
few of a signal's template type parameters from their defaults, and the parameters
you wish to change are near the end of the signal's template parameter list.
For example, if you only wish to change the Mutex template type
parameter of a signal, you might write:
namespace bs2 = boost::signals2; using namespace bs2::keywords; bs2::signal_type<void (), mutex_type<bs2::dummy_mutex> >::type sig;
For comparison, to specify the same type using the signal class directly looks like:
namespace bs2 = boost::signals2; bs2::signal < void (), bs2::optional_last_value<void>, int, std::less<int>, boost::function<void ()>, boost::function<void (const connection &)>, bs2::dummy_mutex > sig;