Re: Garbage collection in C++
On 21 Nov., 21:07, James Kanze <james.ka...@gmail.com> wrote:
The only use of scope guard I've heard to date has referred to a
complex mixture of macros and templates; innovative, in its way,
but something that really could be handled better with better
language support.
That's your opinion. I stated mine.
The only "scope guard" I've seen is Andrei's.
There you go! BTW: It doesn't contain any macros. With lambdas you can
slim this design down (you only need one "implementation class" that
takes a functor) and rvalue references can make the "mutable hack" go
away.
The implementation matters a lot if I have to write it. Or if
I'm picking it up off the net, and it's not part of my compiler.
Well, you don't have to write it yourself (like any other library that
doesn't come as part of the std library).
pointer p by value. That's where a C++0x feature comes into
play.
Along with the rvalue reference. And auto. It looks to me like
it vitally depends on C++0x. And has a very unintuitive way of
being written. And requires a named variable. It's still far
from ideal.
Far from ideal? Well, I suppose it's a matter of taste. Still, you
seem to be exaggerating.
'auto' and rvalue references are not vital to this. But with 'auto'
you don't need a common base clase like it's done in the scope guard
version by Andrei Alexandrescu and Petru Marginean. And with rvalue
references you don't need to declare the 'dismissed' flag mutable.
(This mutably flag is a bit of a move semantics emulation hack.)
[...]. It gets even better if you stick with
std::vector which will become movable in C++0x:
std::vector<double> example3();
This works in C++99. I do it all the time.
The difference is that the language standard doesn't force
compilers to do return value optimization as far as I know.
[...]
And how is that relevant?
Let me explain it to you: You said "works in C++99". It's nice that it
works for you but I like to know what happens when I write stuff like
this. C++0x guarantees that the vector's data won't be copied because
either RVO kicks in or the vector is just moved to its new
destination. I'm sorry If I wasn't clear enough. For me "it works"
implies no copying of the vector's data in this case. That is why it's
relevant.
You left out the most important part: the "library magic".
Actually it's not at all magic. I just didn't consider it to
be interesting enough for this thread. I'm confident that you
[...] are able to implement it by yourself in no time.
I doubt it.
Then, you should read that Dr Dobbs article from 2000 again.
http://www.ddj.com/cpp/184403758
Cheers!
SG