request switch statement with common block

[H. S. Teoh]

On Sat, Aug 03, 2013 at 01:33:44PM -0700, Jonathan M Davis wrote:
> On Saturday, August 03, 2013 12:35:22 H. S. Teoh wrote:
> > On Sat, Aug 03, 2013 at 12:22:53PM -0700, Walter Bright wrote:
[...]
> > > Consider, for example, the scope guard statement in D. It is
> > > extremely useful - but it is an unusual form (doesn't exist in
> > > other languages) and programmers just don't think in those terms.
> > > Andrei & I constantly have to work at 'selling' the benefits of
> > > it. It still hasn't really caught on.
> > 
> > At least it has caught on with me. :) After learning about scope
> > guards in D, I've been plagued with persistent thoughts of "I wish I
> > could use a scope guard here!" every time I work with C/C++ code.
> > 
> > Ironically, though, D's superior design has pretty much eliminated
> > the need for scope guards except in a few rare cases. :-P  They used
> > to be still useful for things like closing files at the end of the
> > block, but struct dtors have pretty much eliminated that use case as
> > well.
> 
> I'm surprised that you'd miss scope in C++ and yet not use it in D.

Well, I miss it more in C than C++, but C++'s manual memory management
does make scope rather attractive. The same goes for D, actually, but
that's largely alleviated due to the built-in GC.


> The only thing that's really missing from C++ that D has that you
> might use in place of scope is finally.

Truth be told, I think scope trumps finally because it localizes the
cleanup statement to the initialization. Sprinkling related code across
two different places is more fragile and bug-prone.


> C++ has RAII just like D does.  There's a much bigger difference when
> comparing against languages which don't have RAII (such as Java or
> C#), but with C++ has RAII.

Yeah, I think I mostly had C in mind when I wrote what I did. :)


> In general, I think that it comes down to a question of whether RAII
> or scope(exit) is more appropriate, and RAII works better in common
> cases (such as closing files or releasing a mutex), wheras scope(exit)
> works better in cases which aren't common (since it doesn't make sense
> to create types just for those cases). RAII also makes more sense in
> cases where you essentially need a reference count before doing the
> action rather than just when exiting the scope (e.g. closing files is
> also a good example of that; a File struct is more flexible than using
> scope(exit) to close the file).

Yeah, with RAII, much of the use cases of scope is eliminated. I'm
mainly working with C at my job right now, which is why I miss scope so
much. C is just so tedious to use due to the amount of manual
baby-sitting required to make things work properly. I still miss scope
in C++ because of the lack of a GC, but otherwise, even C++ doesn't have
that many use cases for scope left.


> I definitely use scope from time to time, but I don't know how
> frequently I use it in comparison to how often I should use it. I was
> actually using scope(success) more until someone pointed out that
> there's an efficiency hit with that as it was putting try-catch blocks
> in places where there wouldn't have been before (as opposed to
> scope(exit) or scope(failure) where you'd be using try-catch blocks if
> you weren't using scope).
[...]

Hmm, I never thought of that. So that limits the use cases of scope
guards even more. :-P


T

-- 
My program has no bugs! Only unintentional features...