[boost] [signals2] 'static initialisation fiasco' issues

Subject: [boost] [signals2] 'static initialisation fiasco' issues
From: elpidio valdez (elpidiovaldez6_at_[hidden])
Date: 2011-09-27 14:39:40

I am trying to build a modular system in which independently compilable cpp
files communicate by signals, but otherwise know nothing about each other at
compile time.

e.g.

 #include "TheRangeFinderSignals.h"
#include "TheProximitySensorSignals.h"
class TerrainMap {
....connect to signals and send signals....
} TheSingletonTerrainMap;

This all works very well except that TerrainMap needs to connect to signals
from its constructor. The signals are static global objects which serve to
exchange data between the independent modules. Unfortunately I have fallen
foul of C++ static initialisation problems. I cannot be certain that the
static signal objects will be created before the modules that use them.

The C++ FAQ recommends wrapping the static variables in a function:

e.g.

EventSignal<void (Gray16Image)> &OnNewDepthFrameAvailable() {

  static EventSignal<void (Gray16Image)> *zzz = new
EventSignal<void(Gray16Image)>;

  return *zzz;

}

This works but it is syntactically messy to use.  All uses of
OnNewDepthFrameAvailable must be replaced with OnNewDepthFrameAvailable().

i.e OnNewDepthFrameAvailable().connect(...)

     OnNewDepthFrameAvailable()(theNewFrame);

Is there any way to avoid this ?  It is not easy to hide the detail.  I
wanted to define a template class to encapsulate the idiom and eliminate the
need for the extra parenthesis.

e.g. SafeStatic< EventSignal<void (Gray16Image)> > OnNewDepthFrameAvailable;

template<type T> class SafeStatic {

  T *obj;

  void operator()(theArgsToSignal) {

    if (!obj) obj = new T;

   obj(theArgsToSignal);

 }

};

The problem is that the Signal template defines a variable arity and
signature operator().  I have no idea how to provide the same signature on
the function call operator of SafeStatic

Any other way around this problem ?