boost signals auto disconnect lambda slot

Question

I'm trying to do this:

boost::signals::connection c = somesignal.connect(
[c]()->void{
    // Do something
    c.disconnect();
})

Will this cause problems?

The connection c is assigned only after connect.

lambda needs to be initialized before connect.

It seems capture by value would not work. However, I can not capture by reference, since c is only a local variable.

If it is not a lambda, I can capture the "somesignal", and call somesignal.disconnect(slot). But in the case of a lambda, the slot is itself.

@FrankOsterfeld No, it's not. But same problem if replace boost by qt. — Min Lin, Mar 14 '14 at 09:48
@sehe yes, it should be able to be invoked out of scope. At that time c is no longer available by reference — Min Lin, Mar 14 '14 at 09:59
I just realized that `connection` != `signal`. I haven't used signals much to date. See my answer — sehe, Mar 14 '14 at 10:00

Igor R. · Accepted Answer · 2014-03-14T12:25:29.283

1

Use extended slot, Signals2 passes the connection object to it. It's designed primarily for thread-safety, but you can utilize it for your purposes as well:

somesignal.connect([](const connection &c)->void 
{
  // Do something
  c.disconnect();
});

(By the way, as opposed to what the title implies, it's actually not an "auto-disconnection", but the manual one. To disconnect slots automatically, one could use the tracking mechanism.)

edited Mar 14 '14 at 12:25

answered Mar 14 '14 at 12:18

Igor R.

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This appears to be called `connect_extended` now – Ell Feb 28 '21 at 06:53

boost signals auto disconnect lambda slot

1 Answers1