Re: [Boost-users] [RFC] Signals bound to phoenix functions

24 Jun 2010


      On Thursday 24 June 2010 09:31:36 Thomas Heller wrote:
...
On Wednesday 23 June 2010 18:50:38 Ovanes Markarian wrote:
...
Stephan, hi!
please see my answer below.
On Wed, Jun 23, 2010 at 5:42 PM, Stephan Menzel
wrote:
...
...
Unless I want to add something. Unfortunately I can't always take
wrap()s output but have to modify a little. In fact, my Queue needs to
be templatized as well, modifying the behaviour of the functor. I have
a template parameter "Calling". When it is true, another function
shall be called by the functor after the method was posted. Now I
wanted to do this by phoenix:
template <bool Calling>
class Queue {
template<typename Handler>
void post(Handler n_handler) {
m_iosrv.post(n_handler);
};
...
template
  boost::signals2::connection
connect(boost::signals2::signal<SlotSignature> &n_signal, SlotFunction
n_method) {
return n_signal.connect(
if_( CallingBack ) [
post(n_method) ,
                                    m_signal_callback()
] .else_ [
m_iosrv.wrap( n_method )
] );
};
...
It is difficult to conclude smth from the code without having a
self-containing example. But my assumption is that in the 'else'-branch
your code does not generate a function object. As far as I can see in the
'if'-branch your code generates a function object using the the
comma-operator (if that operator is overloaded in Phoenix), in the
'else'-branch you just have a normal function call, which is not lazy and
does not return a function-object.
Phoenix statements always return void.
What you want is:
phoenix::if_else( CallingBack, /* then functor */, /*else functor */ )
For reference:
http://www.boost.org/doc/libs/1_43_0/libs/spirit/phoenix/doc/html/phoenix/c
omposite.html#phoenix.composite.operator and
http://www.boost.org/doc/libs/1_43_0/libs/spirit/phoenix/doc/html/phoenix/c
omposite.html#phoenix.composite.statement (There is a note at the end of
that section, for the return value of phoenix statements)
Sorry misunderstood your problem ...
The correct answer is:
post, m_signal_callback() and m_iosrv.wrap need to be 
lazy expressions.
To achieve that for the first two, you can have a phoenix::function wrapper, 
for the last one, you can use phoenix::bind (which can be used for the first 
two as well).