Re: [boost] very simple implementation of Andrei Alexandrescu's ScopeGuard idiom

Subject: Re: [boost] very simple implementation of Andrei Alexandrescu's ScopeGuard idiom
From: Lorenzo Caminiti (lorcaminiti_at_[hidden])
Date: 2012-09-03 21:55:30

On Mon, Sep 3, 2012 at 6:37 PM, Sergey Radionov <rsatom_at_[hidden]> wrote:
> 2012/9/4 Lorenzo Caminiti <lorcaminiti_at_[hidden]>:
>> On Mon, Sep 3, 2012 at 10:28 AM, Stewart, Robert <Robert.Stewart_at_[hidden]> wrote:
>>> Sergey Radionov wrote:
>>>>
>>>> https://github.com/RSATom/finally_execute/blob/master/finally
>>>> _execute.h
>>>>
>>>> based on http://www.drdobbs.com/cpp/generic-change-the-way-
>>>> you-write-excepti/184403758?pgno=2
>>>>
>>>> I know about http://sourceforge.net/projects/loki-lib/ but
>>>> with boost::bind this can be much simpler:
>>>> https://github.com/RSATom/finally_execute/blob/master/README
>>>>
>>>> I've used this in many of my projects, and found it very
>>>> usefull....
>>>>
>>>> don't understand, why this simple solution does not
>>>> contributed already to Boost by someone else... :)
>>>
>>> I created a version, too, but the usage is much simpler.
>>>
>>> Given the following:
>>>
>>> FILE * const file(fopen("test", "r"));
>>> if (file)
>>> {
>>>    // A
>>> }
>>>
>>> Your usage, at A, is:
>>>
>>>    finally_execute _(make_fin_exec(boost::bind(fclose, file)));
>>>
>>> Mine is:
>>>
>>>    scope_guard _(fclose, file);
>>>
>>> As you can see, a little more complication in the component makes
>>> usage much simpler.
>>
>> Boost.ScopeExit allows you to "execute *arbitrary* code when the
>> enclosing scope exits". I don't see how you execute arbitrary code
>> with the above.
> Yep, but in 90% of cases I just need call one function on scope exit,

OK if that's what you need but that's not the problem that ScopeExit
is trying to solve to "call a function on scope exit".

> and in this case ScopeExit will be too cumbersome.
> little example:
>
> void foo()
> {
>    FILE* f1 = fopen( "file1.bin", "rb");
>    if( !f1 ) return;
>    finally_execute close_file1 = make_fin_exec( boost::bind(fclose, f1) );
>
>    FILE* f2 = fopen( "file2.bin", "rb");
>    if( !f2 ) return;
>    finally_execute close_file1 = make_fin_exec( boost::bind(fclose, f4) );
>
>    FILE* f3 = fopen( "file3.bin", "rb");
>    if( !f3 ) return;
>    finally_execute close_file1 = make_fin_exec( boost::bind(fclose, f4) );
>
>    FILE* f4 = fopen( "file4.bin", "rb");
>    if( !f4 ) return;
>    finally_execute close_file1 = make_fin_exec( boost::bind(fclose, f4) );
> }
>
> how it will look with ScopeExit?

If you are willing to use macros (as ScopeExit does), maybe something like this:

#define EXIT_CLOSE(f) \
    BOOST_SCOPE_EXIT(&f) { \
        fclose(f); \
    } BOOST_SCOPE_EXIT_END

void foo()
{
   FILE* f1 = fopen( "file1.bin", "rb");
   if( !f1 ) return;
   EXIT_CLOSE(f1)

   FILE* f2 = fopen( "file2.bin", "rb");
   if( !f2 ) return;
   EXIT_CLOSE(f2)

   FILE* f3 = fopen( "file3.bin", "rb");
   if( !f3 ) return;
   EXIT_CLOSE(f3)

   FILE* f4 = fopen( "file4.bin", "rb");
   if( !f4 ) return;
   EXIT_CLOSE(f4)
}

> what will be more clear?

That depends on your application domain, maybe your developer's tema,
etc so it's your call.

>> http://www.boost.org/doc/libs/1_51_0/libs/scope_exit/doc/html/index.html
>>
>>> There's also Boost.Scope Exit, though it's even more verbose:
>>>
>>>    BOOST_SCOPE_EXIT(&file)
>>>    {
>>>       fclose(file);
>>>    }
>>>    BOOST_SCOPE_EXIT_END
>>>
>>> If there's interest in it, I'd have to seek permission to submit
>>> my library.
>>>
>>>
>>> _____
>>> Rob Stewart                           robert.stewart_at_[hidden]
>>> Software Engineer                     using std::disclaimer;
>>> Dev Tools & Components
>>> Susquehanna International Group, LLP  http://www.sig.com
>>>
>>>
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>>
>>
>> --
>> --Lorenzo
>>
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-- 
--Lorenzo