Re: [boost] try... catch... finally?

From: Alexander Nasonov (alnsn_at_[hidden])
Date: 2007-04-04 16:41:49

Hans Larsen wrote:
> or, putting the code as a parameter to the macro:
> 
> BOOST_SCOPE_EXIT( (hello)(world),
> {
>    // ...
> } );

As Andrey pointed out, any comma inside the block would break your code:

BOOST_SCOPE_EXIT( (hello)(world), { a, b; } )

GNU g++ would report something like:
macro "BOOST_SCOPE_EXIT" passed 3 arguments, but takes just 2.

You could either

BOOST_SCOPE_EXIT( (hello)(world), ({ a, b; }) )

or

BOOST_SCOPE_EXIT( (hello)(world), { (a, b;) } )

but I don't know how to deal with these strange constructs.

> What about using a static variable instead?
It has no significant differences with a global variable.

>          // User code
>          //BOOST_SCOPE_EXIT( (hello)(world) ) // line 1
>          /* Expands to: */
>          static struct args_line1_t { std::string &hello, &world; }  
> args_line1 = { hello, world };
It's incorrect, args_line1 is initialized only once and never
changes. It always points to hello and world existed when a program
reached this point the first time.

> Is the use of __LINE__ correct?  I can't think of a way to break it,  
> which in no way means it's perfect...
It's correct unless you put more than one scope(exit) in one line.

>  >>>> Why do  you need that library and is it absolutely necessary?
>  >>> Because I saw so much exception unaware code.
>  >> I don't see any case of valid exceptions in the use of this library.
>  > Sorry, I don't understand this statement.
> 
> Simply that
> BOOST_SCOPE_EXIT( ... )
> {
>      throw XXX;
> }
> 
> Is invalid by definition.
Indeed, it's almost always invalid. I would never throw from inside
of a scope(exit) block.
But I was talking about exception unware code in pre scope(exit)
era. Developers often don't cleanup resources if an exception is
thrown. The library would help here.

> If you're talking about the fact that you need to get an unknown  
> typename into a local-class (how to know that hello and world are  
> std::string, for example), then the typeof dependency is well  
> justified.  Otherwise, I still fail to see why it is needed.

Yes, typeof is there to bring types of variables into the class.

-- 
Alexander Nasonov
http://nasonov.blogspot.com
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