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: Thomas Heller (thom.heller_at_[hidden])
Date: 2012-07-09 07:12:49

On 07/08/2012 11:16 PM, Ryan wrote:
> Hello,
>
> In upgrading from boost 1.39 to 1.47 I changed my use of the Phoenix
> library (which was within Spirit) to the stand alone Phoenix library.  This
> caused my below code to stop working.
>
> /**** Code Start ***/
> static boost::char_separator<char>  seperator(":");
> boost::tokenizer<  boost::char_separator<char>  >  tokens(s, seperator);  //s
> is a passed in std::string
> std::vector<std::string>  string_tokens;
>
> namespace phx = boost::phoenix;
> //This line fails to compile now.
> std::for_each(tokens.begin(), tokens.end(),
> phx::bind(&std::vector<std::string>::push_back,&string_tokens,
> phx::arg_names::arg1));
> /**** Code Stop ***/
>
> This lead me to three questions.
>
> 1.  What changed about phoenix bind that caused this not to work any more?
I don't know, to be honest. I am surprised this worked at all. push_back 
is overloaded which can't really be handled that well with bind.
>
> 2.  I tried using the lazy version of push_back to bypass the bind issue.
>   In the documentation there are not any examples of multiple algorithm and
> container methods calling each other to show how the arguments of one
> method is passed to another.
>
> std::for_each(tokens.begin(), tokens.end(), phx::push_back(&string_tokens,
> phx::arg_names::arg1));
>
> This compiles but nothing is placed into string_tokens.  So I'm assuming
> the argument from for_each isn't being passed to push_back.  What needs to
> changed in this method call?
I am surprised this even compiles. What you want is to pass a reference 
to string_tokens into the phoenix expression:

phx::push_back(phx::ref(string_tokens, phx::arg_names::arg1)
>
> 3.  Can that entire line of question 2 be replaced with the lazy version of
> the method calls or does the outer most call need to be a non-lazy method?
>
> phx::for_each(phx::arg_names::arg1, phx::push_back(phx::arg_names::arg2,
> phx::arg_names::arg3))(tokens, string_tokens, ???);
>
> If the entire line can be a lazy version then how would I map for_each to
> push_back for arg3?
use phx::lambda for the lambda function phx::for_each shall call:

phx::for_each(phx::arg_names::arg1, phx::lambda(phx::local_variable::
_a = phx::ref(string_tokens))[phx::push_back(phx::local_variable::_a, phx::arg_names::_1)])(tokens);

>
> Any help for these three questions would really be appreciated.

Hope that helps.
>
> Ryan
>
>
>
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