try..catch..pass..finally Was: DMD 0.148 - scope guard

[S. Chancellor]

On 2006-03-01 02:15:35 -0800, "Walter Bright" <newshound at digitalmars.com> said:

> 
> "S. Chancellor" <dnewsgr at mephit.kicks-ass.org> wrote in message 
> news:du376e$1fbf$2 at digitaldaemon.com...
>> Something like this would be equivalent?
>> 
>> Transaction abc()
>> {
>> Foo f;
>> Bar b;
>> Def d;
>> Auto scoped = new Scoper();  //scoped.exit() can be called by the 
>> destructor.  We won't add a finally block.
>> 
>> try {
>> scoped.failures ~= void delegate () { dofoo_unwind(f); }
>> f = dofoo();
>> 
>> scoped.failures ~= void delegate () { dobar_unwind(b); }
>> b = dobar();
>> 
>> scoped.success()
>> } catch (Exception o) {
>> scoped.failed()
>> throw o;
>> }
>> 
>> return Transaction(f, b, d);
>> }
> 
> Should be:
>      f = dofoo();
>      scoped.failures ~= void delegate () { dofoo_unwind(f); }
> etc. Other than that, it looks like it'll work, but it's a lot more 
> code than on_scope. You also need to be sure that the delegates don't 
> refer to any variables declared inside the try block, as those 
> variables no longer exist in the catch block - and the compiler can't 
> catch that error. This isn't a problem with on_scope.

Why would that be the case?  If dofoo() throws an error, that delegate 
would not yet be appended to the failures delegate array.  Thus it 
wouldn't be able to do it's job in the catch block.  I know your and 
derek's order was like this originally, but it seemed like a typo so I 
fixed it.

-S.