Re: [boost] [Bind] Interoperability of bind/mem_fn with transform_iterator

Subject: Re: [boost] [Bind] Interoperability of bind/mem_fn with transform_iterator
From: Daniel Walker (daniel.j.walker_at_[hidden])
Date: 2010-05-04 21:20:24

On Tue, May 4, 2010 at 6:55 PM, Jeffrey Lee Hellrung, Jr.
<jhellrung_at_[hidden]> wrote:
> On 5/4/2010 3:49 PM, Daniel Walker wrote:
>>
>> On Tue, May 4, 2010 at 1:49 PM, Peter Dimov<pdimov_at_[hidden]>  wrote:
>>>
>>> Samuel Debionne:
>>>>
>>>> Anyway, in my opinion, using bind/mem_fn/lambda with transform_iterator
>>>> is a common use case. That would be great to have an option to add a
>>>> default constructor in those libs... or is it to risky ?
>>>
>>> The proper fix would be to make transform_iterator not require a
>>> default-constructible function object, by using boost::optional or an
>>> equivalent.
>>
>> That's a great idea! I took a look at it, and the required changes
>> seem to be minor. I made a ticket and attached a patch.
>> https://svn.boost.org/trac/boost/ticket/4189
>> I ran Boost.Iterator regression tests with gcc 4.2 and it passed without
>> error.
>>
>> Daniel Walker
>
> Maybe you should only conditionally wrap in a boost::optional, e.g., if
> has_trivial_constructor<F> is false

What would that gain? It's a little hairy to implement on old
compilers. I'm not sure that it's worth it.

> (I don't think there's a standard is_default_constructible trait, right?).

Not to my knowledge.

Daniel Walker