• Per =?UTF-8?B?Tm9yZGzDtnc=?= (4/4) Aug 31 2020 I'd appreciate if somebody elaborated a bit on the purpose of the
• H. S. Teoh (24/29) Aug 31 2020 My guess is to be completely exception-safe. For example:
• Per =?UTF-8?B?Tm9yZGzDtnc=?= (2/3) Aug 31 2020 Nice. Thanks.
• Simen =?UTF-8?B?S2rDpnLDpXM=?= (27/31) Aug 31 2020 With this code:

Per =?UTF-8?B?Tm9yZGzDtnc=?= <per.nordlow gmail.com> writes:

I'd appreciate if somebody elaborated a bit on the purpose of the 
compiler flag

     -preview=dtorfields       destruct fields of partially 
constructed objects

"H. S. Teoh" <hsteoh quickfur.ath.cx> writes:

On Mon, Aug 31, 2020 at 08:22:02PM +0000, Per Nordlöw via Digitalmars-d wrote:
 I'd appreciate if somebody elaborated a bit on the purpose of the
 compiler flag
 
     -preview=dtorfields       destruct fields of partially constructed
 objects

My guess is to be completely exception-safe. For example:

	class Resource(T) {
		T* handle;
		this(...) { handle = acquireResource(...); }
		~this() { releaseResource(handle); }
	}

	class ResCollection {
		Resource!A resA;
		Resource!B resB;

		this() {
			resA = new Resource!A(...);
			resB = new Resource!B(...);
		}
	}

If an exception is thrown during the call to `new Resource!B`, the
current behaviour is that resA is not destructed, so there may
potentially be a resource leak.  The abovementioned compiler flag is to
force destruction of resA in case resB fails to be initialized (i.e., as
if you wrote `scope(failure) delete(resA);` after the `resA = ...`
line).


T

-- 
Кто везде - тот нигде.

Per =?UTF-8?B?Tm9yZGzDtnc=?= <per.nordlow gmail.com> writes:

On Monday, 31 August 2020 at 20:34:23 UTC, H. S. Teoh wrote:
 My guess is to be completely exception-safe. For example:

Nice. Thanks.

Simen =?UTF-8?B?S2rDpnLDpXM=?= <simen.kjaras gmail.com> writes:

On Monday, 31 August 2020 at 20:22:02 UTC, Per Nordlöw wrote:
 I'd appreciate if somebody elaborated a bit on the purpose of 
 the compiler flag

     -preview=dtorfields       destruct fields of partially 
 constructed objects

With this code:

struct S1 {
     this(int) {}
     ~this() {
         import std.stdio;
         writeln("~S1");
     }
}

struct S2 {
     S1 s1;
     S1 s2;
     this(int i) {
         s1 = S1(0);
         throw new Exception("");
         s2 = S1(0);
     }
}

void main() {
     S2 a = S2(2);
}

The current behavior is to not destruct the s1 and s2 fields, but 
-preview=dtorfields ensures they will be destructed. I kinda 
expected only s1 to be destructed above, but s2 follows it down 
the drain.

--
   Simen