Re: [boost] Request for review: scope_exit

From: Alexander Nasonov (alnsn_at_[hidden])
Date: 2006-11-27 01:28:07

Matt Gruenke wrote:
> First, a usage example:
> 
>             glob_t result_glob;
> 
>             BOOST_FINALLY__BEGIN
>             {
>                 globfree( &result_glob );
>             }
>             BOOST_FINALLY__END

BEGIN/END variant of BOOST_SCOPE_EXIT exits but I like it less because
POSSIBLY SMALL code IS SURROUNDED by capital letters:

BOOST_SCOPE_EXIT_BEGIN( (result_glob) )
{
    globfree( &result_glob );
} BOOST_SCOPE_EXIT_END;

It's strange that your code compiles because

$ tail -n 8 finally.cpp
int main()
{
    int a, b;
    BOOST_FINALLY__BEGIN
    { a + b; }
    BOOST_FINALLY__END
}

$ g++ finally.cpp
finally.cpp: In destructor
`main()::boost_finally_25::~boost_finally_25()':
finally.cpp:26: error: use of `auto' variable from containing function
finally.cpp:24: error:   `int a' declared here
finally.cpp:26: error: use of `auto' variable from containing function
finally.cpp:24: error:   `int b' declared here

So, you can use only global or static variables inside the block.

> The basic idea is to use the destructor of an instance of a local struct 
> as the mechanism through which the "at scope exit" code gets invoked.  
> In order to facilitate multiple such blocks in the same scope, type and 
> variable names are made unique by appending the source file line number 
> to both names.

SCOPE_EXIT is based on the same idea.

> I should note that this was designed for use in functions, only.  Also, 
> there are some cases in which I've found this unsatisfactory, ...

Can you be more specific about these?

-- 
Alexander Nasonov
http://nasonov.blogspot.com
Take away love and our earth is a tomb.  Robert Browning
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