Re: [Boost-users] [Phoenix] for_each calling push_back for stl containers

Subject: Re: [Boost-users] [Phoenix] for_each calling push_back for stl containers
From: Ryan (boost_at_[hidden])
Date: 2012-07-15 21:30:23

On Sun, Jul 15, 2012 at 1:23 PM, Nathan Ridge <zeratul976_at_[hidden]>wrote:

>
> I don't see why you insist on using phoenix::for_each.
>

I'm trying to gain an understanding of the phoenix library.  This is an
easy example that I have in my code to tear apart.  I know the end result
and there are only two functions that I'm varying.

The advantage of phoenix::for_each over boost::for_each is that phoenix::
> for_each is lazy (it allows you to delay some of the arguments to be
> passed in later). You are not making use of that feature here - you are
> providing all of the arguments up-front, and as a result, you have to
> call the resulting delayed function with no arguments.
>

True.  I'm not taking full advantage of the Phoenix library.  I find it
easier to know when to use a lazy for_each when I see how it plays with
other things.

You should only use the lazy version of a function when you are taking
> advantage of the fact that it's lazy; in other cases it's simpler to use
> the regular, non-lazy version. In this case, you need push_back() to be
> lazy, but not for_each(), so you are complicating things unnecessarily
> by using the phoenix version of for_each.
>

I agree.  Again I view this as a learning experience.  If I started with a
very complicated problem I might not understand the library enough to find
the solution.

> This works just fine, as I've mentioned before:
>
> boost::for_each(tokens, phx::push_back(phx::ref(string_tokens),
> phx::arg_names::arg)));
>

This will probably be the method I go with in the end.

Note that it is not inconsistent that you are using boost::for_each for
> one algorithm, and phoenix::push_back for another. The phoenix:: algorithms
> are exactly like the boost:: algorithms except that they add laziness.
> Since adding laziness complicates the interface of the function, it follows
> that you should only use the lazy version in instances where you actually
> need the laziness.
>

I have no problem using the boost::for_each, std::for_each or the
phoenix::for_each.  Unfortunately, I didn't understand the
phoenix::for_each.

Ryan