Re: [boost] [Bind] How do I get bind to deduce the return type of for_each?

Subject: Re: [boost] [Bind] How do I get bind to deduce the return type of for_each?
From: Daniel Walker (daniel.j.walker_at_[hidden])
Date: 2010-04-19 13:39:53

On Sat, Apr 17, 2010 at 11:50 AM, Roland Bock <rbock_at_[hidden]> wrote:
> Daniel Walker wrote:
>>
>> On Sat, Apr 17, 2010 at 8:58 AM, Roland Bock <rbock_at_[hidden]> wrote:
>>
>>>
>>> Daniel Walker wrote:
>>>
>>>>
>>>> On Sat, Apr 17, 2010 at 7:25 AM, Roland Bock <rbock_at_[hidden]> wrote:
>>>>
>>>>>
>>>>>  for_each(vov.begin(), vov.end(),
>>>>>      bind(for_each< vocType::iterator, function<void (myClass&)> >,
>>>>>         bind<vocType::iterator>(&vocType::begin, _1),
>>>>>         bind<vocType::iterator>(&vocType::end, _1),
>>>>>         protect(bind(&myClass::func, _1))
>>>>>         )
>>>>>      );
>>>>>
>>>>>
>>>>
>>>> Oh yeah, that's a good idea! Instantiate std::for_each with a void
>>>> boost::function! That's a portable solution as well, since bind and
>>>> function are available on practically any compiler, even ancient,
>>>> substandard ones.
>>>>
>>>> Daniel Walker
>>>>
>>>>
>>>>
>>>
>>> Thanks :-)
>>>
>>> Btw, could I do the same with tr1::bind? What would be the equivalent of
>>> boost::protect?
>>>
>>
>> Yeah, you can do the same thing in TR1. Instead of boost::protect, you
>> can just use tr1::function, again. :)
>>
>>   for_each(vov.begin(), vov.end(),
>>         bind(for_each< vocType::iterator, function<void (myClass&)> >,
>>            bind<vocType::iterator>(&vocType::begin, _1),
>>            bind<vocType::iterator>(&vocType::end, _1),
>>            function<void(myClass&)>(bind(&myClass::func, _1))
>>            )
>>         );
>>
>> Actually, I once wrote a functional_cast (analogous to lexical_cast)
>> that did something like that. It's in vault.
>>
>> Daniel Walker
>>
>
> OK, got it, the function object kind of digests the inner _1 before the
> outer bind can lay its fingers on it :-)

Exactly. :) And moreover, with respect to TR1/c++0x,
is_bind_expression has not been specialized for the function object's
type, so it's not treated as a sub-bind expression.

>
> Just took a look at the polymorphic_function and functional_cast. I'll have
> to try and remember it, because I am sure I had use cases for that in the
> past (obviously solved them in another way). How would you apply them to the
> current topic?

Oh, I was just mentioning it as an aside, because the idiom looks
similar; e.g. wrapping things with function<signature>(object).
functional_cast can be used to change the signature in order to
achieve a polymorphic effect when the underling object can support
multiple call signatures. But that's not the issue here.

Daniel Walker