[Boost-users] Re: Intoductory Boost Presentation

From: Jorg Brown (jorg_at_[hidden])
Date: 2003-11-11 14:25:03

Matt -

The corrected code is indeed much better.  May I suggest using
std::vector instead of vector?

The typedef of FooPtr is fine, it turns out; it's the typedef of struct
Foo that was the problem.  I had declared Foo within main as well, and
that blocks the use of boost::shared_ptr on it.  As long as Foo is
declared at global scope, all is well.

As for the correct output, my compiler gives me 3, then 2, then 1.  I
talked it over with a friend, and I guess the order of the 2 vs 1 is
undefined, and depends on your STL's implementation of std::vector.

As for the crazy aunt in the basement, the comment was meant for an
internal list that only 20-30 people are on, not meant for general
consumption, and probably merits an extra thread by itself.  Put simply,
using boost can generate a surprising amount of code and overhead.  This
is true of STL as well.  There are even some good books describing STL;
I happen to like Plauger/Stepanov/Lee/Musser, as well as Jasoutis.  But
nowhere do I see any reference as to what the downsides are - and
nowhere do I see any concise explanation of why an enormous amount of
code (660 bytes in an optimized, no-symbols build) is generated when I
say something as simple as

void Testbed(void) {
   boost::function<void> SimpleFPtr(&Testbed);
}

When you say "I was trying to generate interest in these libraries and
thus didn't want to focus too much on the negatives", I can understand
your point of view, but what I see in real life is that people start
using boost::function everywhere they used to use plain old function
pointers, with nary a clue that their code size just exploded with no
benefit.

But like I said, it's worth a whole other thread.

Thanks for fixing the code and responding so quickly!

jorg

-----Original Message-----
From: "Matt S Trentini" <matt_s_trentini_at_[hidden]>
Reply-To: Boost Users mailing list <boost-users_at_[hidden]>
Date: Tue, 11 Nov 2003 23:19:12 +1100
To: boost-users_at_[hidden]
Subject: [Boost-users] Re: Intoductory Boost Presentation

Heya Jon,

Ah, the smart_ptr example, I knew that would come back to bite me!  ;)
I
changed this example at the last minute in an effort to simplify but, as
your co-worker correctly points out, there are many errors in it.

The correct code is below though the graphic requires change (yes, I
could
have change the list.push_front() to a push_back but I like to see the
variety!).

    int main()
    {
        typedef boost::shared_ptr<Foo> FooPtr;
        vector<FooPtr> foo_vector;
        list<FooPtr>   foo_list;

        FooPtr foo_ptr( new Foo(1) );
        foo_vector.push_back( foo_ptr );
        foo_list  .push_back( foo_ptr );

        foo_vector.push_back ( FooPtr( new Foo(2) ) );
        foo_list  .push_front( FooPtr( new Foo(3) ) );
    }

You'll notice that I left the typedef in there.  I can't find anything
in
the standard (or with google) about it being illegal in main, nor does
my
compiler emit any warnings.  Can anyone shed some light on this?

And I've got to disagree with your friend about the correct ordering -
the
expected output is 3, 1, 2 (Remember that foo_ptr gets deleted first).

I'll endeavour to fix this example up and upload the changes over the
next
couple of days.

As for these comments:

> > The rest of the pages have the classic boost downfall: they
> > don't discuss any of the pitfalls, performance problems, or
> > code bloat issues, which frankly, seem like the "crazy aunt
> > in the basement" of boost.

I'll defend myself on two fronts.  First, it's an introductory
presentation - I was trying to generate interest in these libraries and
thus
didn't want to focus too much on the negatives.  Secondly, I _did_ cover
some of those points - like all good presentations not everything is
contained in the bullet points.

Thanks for the feedback though, it's helping to make this presentation
better!

Cheers,
Matt

PS If there are any other problems that you or your co-worker have found
please don't hesitate to report them!

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