Re: [Boost-users] [Bind] Understanding protect

Subject: Re: [Boost-users] [Bind] Understanding protect
From: Thomas Heller (thom.heller_at_[hidden])
Date: 2012-03-28 06:13:07

On 03/28/2012 11:45 AM, Robert Jones wrote:
> On Wed, Mar 28, 2012 at 10:04 AM, Thomas Heller
> <thom.heller_at_[hidden]>wrote:
>
>> On 03/28/2012 09:47 AM, Robert Jones wrote:
>>
>>> On Tue, Mar 27, 2012 at 8:24 PM, Thomas Heller
>>> <thom.heller_at_[hidden]>**wrote:
>>>
>>>   You might also want to consider phoenix::lambda, it is like protect, but
>>>> slightly more powerful.
>>>> your example would then read:
>>>> #include<boost/phoenix.hpp>
>>>>
>>>> int main( )
>>>> {
>>>>      std::vector<int>   v;
>>>>      v += 0,1,2,3,4,5,6;
>>>>      using boost::phoenix::bind;
>>>>      using boost::phoenix::lambda;
>>>>      using boost::phoenix::placeholders::****_1;
>>>>      using boost::phoenix::local_names::_****1;
>>>>
>>>>
>>>>      for_each( v.begin( ), v.end( ),
>>>>          bind(g, lambda(_a = _1)[bind(f, _a)]));
>>>>
>>>>      return 0;
>>>> }
>>>>
>>>>
>>>>   Please don't remind me! I'd love to, but I'm stuck in the antediluvian
>>> days
>>> of 1.37!
>>>
>>> - Rob.
>>>
>> Ouch. In that case, protect should work just fine.
>> Here is a complete and working example:
>> https://gist.github.com/**2224915
>

>
> Hi Tom
>
> Thanks for the time you've spent on this- much appreciated.
>
> I can see where you're going with this approach, however if I've understood
> it correctly it
> sidesteps the hard bit in that the function g() now takes a unary callable
> and a value. My key
> constraint here is that g() MUST take a nullary callable object, and hence
> the bind machinations
> MUST produce a fully bound, unevaluated, nullary callable object.
>
> I feel like I'm banging-on a bit here - sorry!
Ha, no problem, I enjoy solving such problems :)
After jumping through all kinds of different hoops, I updated the gist:
https://gist.github.com/2224918

I hope this fits your usecase better :) The original function is 
unchanged, I just added the trampoline to rebind the bound functor. 
Well, not the most elegant solution, but might work.

>
> Thx, Rob.
>
>
>> Note that I had to get rid of the template. free template functions are a
>> pain to bind, you would need to somehow cast it to the correct function
>> type, which is unnecessarily clutter, and gets worse in your
>> case. I suggest using functors, there, templates are not a problem at all:
>> <https://gist.github.com/**2224920
>>  <

>> https://gist.github.com/**2224920
>>
>>
https://gist.github.**com/2224918
>
>> To sketch the full picture, phoenix is able to handle that in a saner
>> fashion (sorry for the plug, take it as future reference, I don't want to
>> make your life miserable):
>>
https://gist.github.com/**2224920
>
>> Note that in the phoenix solution, bind is not necessary anymore. Phoenix
>> is able to adapt (even templated) functions to know how to lazily evaluate
>> them.
>>
>>
>
>
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