Re: [boost] [local] Review

Subject: Re: [boost] [local] Review
From: Thomas Heller (thom.heller_at_[hidden])
Date: 2011-11-18 16:49:31

On 11/18/2011 03:27 PM, Jeffrey Lee Hellrung, Jr. wrote:
> On Fri, Nov 18, 2011 at 12:02 PM, Thomas Heller
> <thom.heller_at_[hidden]>wrote:
>
>> On 11/18/2011 01:27 PM, Jeffrey Lee Hellrung, Jr. wrote:
>>
>>> Thanks for the review, Thomas!  I just have a couple comments.
>>>
>>> On Fri, Nov 18, 2011 at 10:49 AM, Thomas Heller
>>> <thom.heller_at_[hidden]>wrote:
>>> [...]
>>>
>>>> Local Blocks:
>>>> I can't see the value in that one. The example in the documentation
>>>> doesn't help either, as those things are easily detected by any modern
>>>> compiler, with the appropriate warning levels (ok, not in the assert
>>>> case,
>>>> but for other boolean contexts at least gcc does).
>>>>
>>>>
>>> I *believe* there has been an instance in my own code where I had to
>>> const_cast a range to coerce a range algorithm to use const_iterator's for
>>> efficiency reasons...or something like that.  I don't remember the details
>>> of the situation, but I can imagine instances where const access to an
>>> object would be more efficient than mutable access, e.g., if mutable
>>> access
>>> via operator[] must return a proxy.  It can be difficult to guarantee in
>>> general that the compiler would optimize a
>>> syntactically-mutable-**semantically-const access into the equivalent
>>> syntactically-const access.
>>>
>>
>> I see. But why do you need local blocks to achieve that?
>>
>
> I don't.  I could just const_cast use of the variable everywhere I want it
> const-qualified.  Or define a reference-to-const to the same effect.  ...or
> use a local block.
>
> You just sounded like you were angling for a legitimate use case for local
> blocks, and I tried to supply a plausible (if rare) one.

Right, and I am still thinking that having things like:
{
    auto const & const_ref_to_object = ...
}

is preferrable (For C++03, replace it with the proper call to BOOST_AUTO 
or repeat the type).
And if you really want a new, independent scope, why not just create a 
new function to make your intention even clearer. Can't think of a 
unique name for that? Hey, there are namespaces.
IMHO, C++ already provides all necessary tools to express what local 
block does.