Re: callback design question

"mliptak" <>
1 Mar 2007 04:26:54 -0800
On Mar 1, 12:17 pm, "dasjotre" <> wrote:

On 1 Mar, 07:19, "mliptak" <> wrote:

I have been using libsigc/signals for several years
and I warmly recommend it.

So I gave it a try and instead of using virtual functions I used the
But I gained nothing in terms of performance and also the interface
remained pretty much the same.
So what's the rationale behind using signals / slots?

signals/slots is a very simple library.

you have much less restrictive interface with signals than with
abstract bases.

struct my_interface
    virtual void fun1(A &)=0;
    virtual void fun2(B &)=0;


with this approach you have to implement both functions even if
you don't use one of them

You can do the default implementation in the base class as well,
instead of pure virtuals..

signal<void (A&)> asignal;
signal<void (B&)> bsignal;

slots are arbitrary function objects
you can connect any function object that is convertible to
the slot

void fun(A&);
struct T
void fun(A&);};

T t;
asignal.connect(bind(&T:fun, &t, _1));

you can bind extra arguments and adapt
interface to fit the signal.

void my_fun(A & a, int n);
asignal.connect(bind(&my_fun, _1, 4));

you have much more robust
and functional connection management.

void my_fun1(B &);
connection con = bsignal.connect(bind(&my_fun1, _1));

using signals::trackable and signals::scoped_connection you
can have automatic connection management

you can group/order slots. you can chain signals. you can
collate results.

now, of course you can implement all that functionality yourself.
the point is that you don't have to since someone else has done
it already.

Thanks for the explanation.
I think I just did not see the use for all this because I did not come
over a realworld application where this could be a perfect fit.

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