Re: [sigc] Interesting minor libsigc++ 2 problems

[Jeff Franks <jcf tpg com au>]

Murray Cumming wrote:

> These are not big problems, but they are interesting when porting to
> libsigc++ 2:
>
> 1. In libsigc++ 1.2 you can do  button.signal_clicked().connect(*this,
> &Gtk::Widget::hide)
> but in libsigc++ 2 you need to write a separate intermediate method to
> handle the signal and then call hide().
>  
I came across this problem and found that using an static_cast to cast 
the "this" pointer to Gtk::Widget pointer works, but it really shouldn't 
be necessary.

button.signal_clicked().connect(sigc::mem_fun(static_cast<Gtk::Widget*>(this), &Gtk::Widget::hide));


> 2. In libsigc++ 1.2 you can override a method like so:
>  void do_something(const Slot0<void>& slot);
>  void do_something(const Slot1<void, int>& slot);
> but in libsigc++ 2 that is ambiguous when you try to call
> do_something().
>
> Sorry for not giving actual compiler errors - I'm rushed.
>  
This is  a problem. I haven't written any overloaded functions that take 
a sigc::slot argument and so I never picked up on this before. This 
seems to be the problem. The sigc::slot<void> argument resolves to:

sigc::slot<void, sigc::nil, sigc::nil, sigc::nil, sigc::nil, sigc::nil, 
sigc::nil, sigc::nil>

and the sigc::slot<void, int> argument resolves to

sigc::slot<void, int, sigc::nil, sigc::nil, sigc::nil, sigc::nil, 
sigc::nil, sigc::nil>

and the compiler sees these as ambiguous.

The only way around this ambiguity is to write code like this, for 
example for a class Window:

void do_something(const sigc::bound_mem_functor0<void, Window>& slot);

void do_something(const sigc::bound_mem_functor1<void, Window, int>& slot);

which is very unsitely, or use some typedefs

typedef  sigc::bound_mem_functor0<void, Window> SomeSlot;
void do_something(const SomeSlot& slot);

typedef  sigc::bound_mem_functor1<void, Window, int> SomeOtherSlot;
void do_something(const int> SomeOtherSlot& slot);

Is this really necessary? Could we have some intermedate sigc::slot0 and 
sigc::slot1 classes or does libsigc2 recommend the use of 
bound_mem_functorN<> directly.

Jeff Franks.