Protection to use for the signal string mixin.
string mixin for creating a signal.
The signal implementation, not providing an emit method.
Full signal implementation.
<a href="http://www.boost.org/LICENSE_1_0.txt">Boost License 1.0</a>.
Copyright Robert Klotzner 2012 - 2014.
Signals and Slots are an implementation of the Observer pattern
Essentially, when a Signal is emitted, a list of connected Observers (called slots) are called.
They were first introduced in the Qt GUI toolkit, alternate implementations are libsig++ or Boost.Signals2 similar concepts are implemented in other languages than C++ too.