scope(success) lowered to try-catch ?

[Timoses]

On Sunday, 17 June 2018 at 10:58:29 UTC, Cauterite wrote:
> Hello,
> I'm not sure whether I'm missing something obvious here, but is 
> there a reason for scope(success) being lowered to a try-catch 
> statement?
> I would have expected only scope(exit) and scope(failure) to 
> actually interact with exception handling, while scope(success) 
> simply places code on the path of normal control flow.
>
> Example (windows x32):
>
> ---
>
> // main.d
> void main() {
> 	scope(success) {}
> }
>
>> dmd -betterC main.d
> Error: Cannot use try-catch statements with -betterC
>
> ---
>
> Regardless of whether -betterC is used, you can see in the 
> disassembly that having a scope(success) anywhere in the 
> function causes the SEH prologue to be emitted in the code.
>
> Is there a reason scope(success) needs to set up for exception 
> handling?
> Or is this a bug / potential enhancement ?

In Andrei's book 'The D Programming Language' the following is 
written:

{
     <statement1>
     scope(success) <statement2>
     <statement3>
}
is lowered to
{
     <statement1>
     bool __succeeded = true;
     try {
         <statement3>
     } catch(Exception e) {
         __succeeded = false;
         throw e;
     } finally {
         if (__succeeded) <statement2> // vice-versa for 
scope(failure): `if (!__succeeded) ...`
     }
}

If it weren't and it would simply be integrated one would have to 
write

     potentiallyThrowingFunc();
     scope(success) {...};

I suppose? And this seems like breaking how scope works with 
failure and exit?!