gmane.comp.lib.boost.announce

dan marsden | 13 Apr 22:24

Egg review period extended until April 20th

Hi All

The Egg review has run for 2 weeks now with zero reviews, which is obviously
disappointing. There has been some good and pretty thorough discussion, and
a couple of promises of reviews. As such, I'm extending the review period
by 1 week until 20th April 2008.

Please do post a review if you have any interest in this library. In case anybody
is unsure, in the case of zero votes being posted, the default result will be
a rejection. Please lets make sure we don't have to fall through to this default case.

Introduction:
    It is not so easy to define Function Objects
    especially if you want to support Boost.ResultOf and Boost.Lambda.
    Therefore, as Boost provides iterator_facade and iterator adaptors,
    Egg provides function_facade and function adaptors.

Egg provides the following features:

    * Workaround for the Forwarding Problem
        http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2002/n1385.htm

    * Helpers to build Function Objects:
        * egg::function and egg::function_facade provides the way to
          build Function Objects which supports Boost.ResultOf and Lambda.

    * Function Objects Adaptors(in other words, higher-order functions):
        * egg::curryN supports the currying.
        * egg::pipable emulates extension methods(C#).
        * egg::fuse/unfuse emulates variadic functions.

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Daniel Walker | 15 Apr 02:40

Re: Egg review period extended until April 20th

On Sun, Apr 13, 2008 at 4:26 PM, dan marsden <danmarsden <at> yahoo.co.uk> wrote:
> Hi All
>
> The Egg review has run for 2 weeks now with zero reviews, which is obviously
> disappointing. There has been some good and pretty thorough discussion, and
> a couple of promises of reviews. As such, I'm extending the review period
> by 1 week until 20th April 2008.

OK, I still don't want to give a formal review, because I haven't
looked at the whole library and I don't want to be unfair. However, I
sent some comments off-list to Shunsuke, and he asked me to post them
here. As he pointed out to me, it's the Boost way! 

I really do think that Egg is technologically solid. If the list is
slow to show interest, I think that's not a reflection of some
technical concern, but perhaps it's a sign of usability hurdles... In
other words, how do you convince users that using the library would
make their lives easier? How do you sell the library?

Approaching the library for the first time, as a new user as much as a
potential reviewer, it seemed to me that Egg overlaps a great deal
with existing Boost libraries and with C++0x. I constantly found
myself asking: "Why would I want to learn this? Can't I just use bind?
Yes, this is better than writing a function, but how is this any
better than just writing a class with operator()?" That last question
was the show stopper for me; I don't have the time, energy or
inclination to learn a new paradigm for writing functors unless there
is a strong motivating need or big potential payoff. Remember,
fundamentally, the raison d'etre of Boost is to increase productivity.
At least, that's what the FAQ says.  And in reality, if this wasn't

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shunsuke | 15 Apr 07:35

Re: Egg review period extended until April 20th

Daniel Walker wrote:
 > OK, I still don't want to give a formal review, because I haven't
 > looked at the whole library and I don't want to be unfair. However, I
 > sent some comments off-list to Shunsuke, and he asked me to post them
 > here. As he pointed out to me, it's the Boost way! 

Thank you, Daniel.

 > I really do think that Egg is technologically solid. If the list is
 > slow to show interest, I think that's not a reflection of some
 > technical concern, but perhaps it's a sign of usability hurdles... In
 > other words, how do you convince users that using the library would
 > make their lives easier? How do you sell the library?

I probably failed to sell the library.

 > Approaching the library for the first time, as a new user as much as a
 > potential reviewer, it seemed to me that Egg overlaps a great deal
 > with existing Boost libraries and with C++0x. I constantly found
 > myself asking: "Why would I want to learn this? Can't I just use bind?

egg::lazy is useful.
`lazy_plus(lazy_plus(_1, 3), lazy_plus(_2, _1))` is much more
readable than an expression using bind.

 > Yes, this is better than writing a function, but how is this any
 > better than just writing a class with operator()?" That last question
 > was the show stopper for me;

It depends on some conditions:

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Daniel Walker | 22 Apr 00:18

Re: Egg review period extended until April 20th

On Tue, Apr 15, 2008 at 1:35 AM, shunsuke <pstade.mb <at> gmail.com> wrote:
> Daniel Walker wrote:
<snip>
>  > struct my_plus
>  > {
>  >    template<class> struct result;
>  >    template<class Me, class X, class Y>
>  >    struct result<Me(X,Y)>
>  >        : boost::remove_cv<X>
>  >    { };
>  >
>  >    template<class X, class Y>
>  >    typename result<my_plus(X,Y)>::type
>  >    operator()(X x, Y y) const
>  >    {
>  >        return x + y;
>  >    }
>  > };
>  >
>  > To my eye, I can't see how Egg makes things that much easier. It
>  > doesn't look particularly helpful.
>
> I was feeling annoyed that I had to write `typename result<my_plus(X,Y)>::type`.
> Also, your `result<>` implementation is wrong.
> It is error-prone to write ResultOf-conforming FunctionObject without some indirection.

How is this result<> implementation wrong? I'm not convinced that
writing result_of compatible functors is that error prone, but if I
made a mistake here, that would pretty much prove your point.

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