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digitalmars.D - nothrow and Throwable?

reply Manu <turkeyman gmail.com> writes:
So, I've never used an exception before, but I guess there's a first time
for everything :P

It seems to be that `Throwable` transcends `nothrow`...
Other than proving code correct-ness, the point of `nothrow` as I see it,
is to inform the compiler that it doesn't have to synthesise unwind tables
for everything in no-throw land... but since Throwable can pass through
`nothrow` territory, how are any RAII objects cleaned up while it unwinds?

void code() nothrow
{
  RAII something;

  doesntThrow();

  // destroy something
}

void  doesntThrow() nothrow
{
  try
     canThrow();
  catch (Exception)
  {
    // catch exceptions from canThrow
  }
}

void canThrow()
{
  throw new Throwable();
}


I expect that an unwind table should not be generated for code(), and so
`RAII something` should not be tidied up if `doesntThrow` actually does
throw... is that what's going on here?

I guess the idea is that Throwable is intended to never be caught, and so
we don't really care about tidying up since an abort is imminent?
Am I reading this correctly... or is it actually that unwind tables are
just always generated for everything, even `nothrow` things?
Apr 06
next sibling parent reply Olivier Pisano <olivier.pisano laposte.net> writes:
Hello,

I suppose this is because a nothrow function cannot throw an 
Exception, but can throw an Error.
Apr 06
parent Manu <turkeyman gmail.com> writes:
Ah, I didn't see Error... but yes, this is my hypothesis, I just wanted to
confirm if it's correct.
Can I expect unwind tables are not generated for nothrow functions?

On Mon, 7 Apr 2025 at 14:06, Olivier Pisano via Digitalmars-d <
digitalmars-d puremagic.com> wrote:


 Hello,

 I suppose this is because a nothrow function cannot throw an
 Exception, but can throw an Error.
Apr 06
prev sibling parent Steven Schveighoffer <schveiguy gmail.com> writes:
On Monday, 7 April 2025 at 03:46:08 UTC, Manu wrote:

 So, I've never used an exception before, but I guess there's a 
 first time for everything :P

 It seems to be that `Throwable` transcends `nothrow`...
 Other than proving code correct-ness, the point of `nothrow` as 
 I see it,
 is to inform the compiler that it doesn't have to synthesise 
 unwind tables
 for everything in no-throw land... but since Throwable can pass 
 through
 `nothrow` territory, how are any RAII objects cleaned up while 
 it unwinds?


https://www.schveiguy.com/blog/2022/05/comparing-exceptions-and-errors-in-d/

-Steve
Apr 06