On Wednesday, 4 March 2015 at 17:19:31 UTC, Steven Schveighoffer
wrote:
On 3/4/15 11:32 AM, "Marc =?UTF-8?B?U2Now7x0eiI=?=
<[email protected]>" wrote:
On Wednesday, 4 March 2015 at 15:43:15 UTC, Steven
Schveighoffer wrote:
On 3/4/15 8:43 AM, Shachar Shemesh wrote:
I'd expect A's destructor to run, which does not seem to be
the case.
I believe destructors are not run when you throw inside a
constructor.
So plan to deallocate if the ctor throws:
a = A(var + 1);
scope(failure) destroy(a);
The spec says [1], that the first write to a field in a class's
constructor is a construction, not an assignment. I assume
this applies
to structs as well. If so, this implies that the compiler
already knows
at each point which fields are already constructed. Why
doesn't it
automatically insert appropriate destructor calls then?
[1] http://dlang.org/class.html#field-init
That is talking about initializing immutable fields.
That's true, but I was going to argue that if the compiler is
able to check this for immutable fields, there is no reason why
it couldn't also do it for mutable ones. But now I see that it
only uses an imprecise heuristic that is probably too coarse to
extend it to mutable fields. In fact, I even found a loop-hole,
which I've filed here:
https://issues.dlang.org/show_bug.cgi?id=14245
The dtor is not called when the exception is thrown, but this
doesn't seem to be in the spec (I don't remember where I read
it, but I'm sure it's an intentional decision). D provides a
mechanism to destroy partially constructed objects, use
scope(failure).
Oh no, another hidden trap :-( `scope(failure)` is only a
workaround if you're aware of it. I think the heuristic for
immutable fields could be adapted to be applicable to mutable
fields: the first assignment to a field must not be inside a loop
or behind a label.
