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

Subject: Re: [Boost-users] [Bind] Understanding protect
From: Robert Jones (robertgbjones_at_[hidden])
Date: 2012-03-28 05:45:00

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 <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!

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/**2224920 <https://gist.github.com/2224920>>
> https://gist.github.**com/2224918 <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 <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.
>
>