On 6/17/18 8:24 AM, Timoses wrote:
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?
I think the request isn't to integrate the code immediately, but to do:
{
<statement 1>
<statement 3>
<statement 2>
}
and be just fine. I think the reason the scope(failure) is done that way
is likely for proper exception chaining in case one of the scope
statements throws.
-Steve
