Re: [Boost-users] [signals] Automatic connection management and MT

From: Timmo Stange (ts_at_[hidden])
Date: 2007-02-06 13:49:46

Douglas Gregor wrote:

[Setting up a signal with tracking support from within a constructor]

> Does enable_shared_from_this help at all?

I don't think you can safely use it in a constructor to acquire a
shared_ptr to yourself, right? It would go out of scope when the
constructor exits and your object will be destroyed. One would have
to provide a factory function, which is what Frank wanted to avoid.

I have a few questions about your Signals implementation, which you
could perhaps answer best:

The templated signalN::disconnect allows disconnection by "slot",
which the docs say elsewhere is difficult to achieve, because of
the problem to compare the target function objects. The Boost
Function agrees with this, but mentions that Signals knows "a
way around it". Now what the implementation seems to do is to
simply call operator== on the target function objects. That frankly
leaves me somewhat confused. I understand that it should work
when the functions are reference wrapped (which will be always
the case when the slot target is a signal itself). We could simply
mimic the original implementation, but I sure would feel better
if I understood what it is going on.

Does storing the combiner in Any really help fighting code bloat
as mentioned under "Type Erasure" in the docs? It is only used
in the signal template. It's copied and invoked, the former by
utilizing the any copy constructor which is templated (resulting
in more code for the heap storage, not in less) and the latter
by using unsafe_any_cast, which effectively gives you a pointer
to the original type and the actual invocation should therefor
result in the same code. I would prefer storing the combiner
directly to avoid the any-related heap allocations, but I don't
have access to a large variety of compilers to check the code
size differences.

As a more general question, do you think that declaring trackable
deprecated and only providing it for backwards-compatibility is
a good solution?

Regards

Timmo Stange