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Subject: Re: [boost] Rave for proposed Boost.Local (functions)
From: Thomas Heller (thom.heller_at_[hidden])
Date: 2011-02-02 02:00:08

Gregory Crosswhite wrote:

> Hey everyone,
> The purpose of this e-mail is to rave about Lorenzo's proposed
> Boost.Local library in the hopes of inspiring people to start the review
> process for it. :-)
> I have been experimenting with using this library in my own code, and it
> has been a godsend for me. In one of the projects I have been working
> on I ran into many situations where I needed to call a higher-order
> function with a closure, and the closure was just complicated enough
> that I couldn't use Boost.Lambda. Before using this library I
> frequently found myself either writing a lot of extra code to
> work-around the need for a higher-order function, or writing a lot of
> boilerplate to create classes that would only be used by a single
> function in order to create a function object. This library has let me
> write the closures that I need in a fairly painless fashion and so has
> made my life a lot easier!

I would be interested in what limitations you ran into using Boost.Lambda
and if you are aware of the recent efforts that were put into Boost.Phoenix?

> To my mind this example looks a lot clearer if you reformat it as follows:
> (void) (add)(
> (double)(num)
> (const bind)((factor))
> (bind)((&sum))
> )
> ) {
> sum += factor * num;
> std::clog<< "Summed: "<< sum<< std::endl;
> add(100.0);

As far is a am concerned, I still find this syntax overly verbose.
I do realize though that this is just a toy example. For better comparison,
Here is how the same thing would like in Boost.Phoenix:

boost::function<void(double)> add
        ref(sum) += factor * _1,
        std::clog << var("Summed: ") << sum << std::endl

Despite the Local Blocks and Local Exits feature, I can't see much
difference to the already existing lambda libraries.
I just looked through the Boost.Local documentation and immediately
navigated to the "Alternatives" section and its not really correct regarding
the features of Boost.Lambda and Boost.Phoenix. I am specifically talking
about the "Bind variables in scope" and "Program body using usual C++
syntax" part. The last is debatable, but how are the above examples (both of
Boost.Local and Boost.Phoenix) not C++ syntax?
Can you highlight the advantages/disadvantages again?

> Cheers,
> Greg
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