Re: [sigc] How does std::function<> work with libsigc++

[Chris Vine <chris cvine freeserve co uk>]

On Mon, 29 Jul 2013 20:44:02 +0200
Kjell Ahlstedt <kjell ahlstedt bredband net> wrote:
> > Wouldn't it be cleaner to just (or also) add a specific
> > connect(std::function<>) method overload that did this
> > automatically?
> Sure. I wish I knew how to do it. sigc::track_obj() forces you to 
> manually specify which trackable objects the functor contains. This
> is not nearly as nice as the automatic detection of trackable objects
> in the rest of libsigc++. The enormous use of C++ templates in
> libsigc++ is near, or even beyond, the limits of my comprehension.

I have to say I disagree with that.  One of the banes of libsigc++ is
that it makes any slot for a non-static method of a class deriving
from sigc::trackable as a tracked slot, which is sometimes what you do
not want.  It is better to enable the user to choose when constructing
the slot.

I also would not encourage passing of std::function objects.
sigc::slot, when passed a callable object (such as a lambda expression
or the return value of std::bind), will perform type erasure on it in
the same way that std::function does.  To do it twice (by passing a
std::function object to sigc::slot) results an unnecessary memory
allocation and an additional and unnecessary virtual dispatch.

Chris