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From: Andrei Alexandrescu (See Website For Email) (SeeWebsiteForEmail_at_[hidden])
Date: 2006-03-09 15:12:31

Alexander Nasonov wrote:
> Pavel Vozenilek <pavel_vozenilek <at>> writes:
>> It is dog-slow: the small example takes over minute!!!! on
>> Athlone XP 2200+ (no optimisations enabled).
>> Intel is known for being slow on heavy templatized code
>> and its preprocessor processing is exponential.
> Unless you passed a lot of variables to BOOST_FINALLY_BEGIN,
> it's not PP, it is Boost.Typeof that is very slow.
>> Mr. Alexandrescu had suggested something like that
>> to be included in the language (as a killer feature
>> not seen in mainstream languages). Specifically,
>> he suggested:
>> on_block_exit { .... code .... }
>> on_block_success { ... code ... }
>> on_block_failure { ... code ... }
> Cool, I didn't know this.
> Is there any proposal for this?

Thank you Alexander for emailing me about this thread.

There isn't, at least not for C++. I convinced Walter Bright to
implement the constructs in D, and helped him write this doc:

Alexander asked me what I think of his implementation, and IMHO it is
superior, and closer to intent, than our original ScopeGuard was. The
fact that you can write arbitrary code inside the scope of interest, and
that code has access (albeit through a less than transparent mechanism)
to the local variables, is very useful for implementing exception-safe
code easily and expressively. For example, the D examples in Walter's
article can be easily translated into C++ (using Alexander's lib) with
only little loss in terseness and clarity.


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