Destructors and static array assignment

[Kenji Hara via Digitalmars-d]

At least there's a dmd bug.

For such static array assignment, dmd should use druntime function, but
instead plain memory copy operation used.
https://github.com/D-Programming-Language/dmd/blob/master/src/e2ir.c#L2920
https://github.com/D-Programming-Language/dmd/blob/master/src/e2ir.c#L2945

And, even after the bug is fixed, I think it's debatable behavior whether
an element-wise assignment should call opAssign on each elements, because
it can be a kind of optimization.

Related issue: https://issues.dlang.org/show_bug.cgi?id=8931

Kenji Hara


2015-07-20 23:18 GMT+09:00 David Nadlinger via Digitalmars-d <
digitalmars-d at puremagic.com>:

> Hi all,
>
> I was about to fix an issue with postblits/destructors in LDC when I
> stumbled upon the following vexing behaviour in DMD (both 2.067.1 and
> master):
>
> ---
> uint dtorCount;
>
> struct S {
>     uint x;
>     void opAssign(const ref S rhs) { assert(false, "Not called"); }
>     ~this() { ++dtorCount; }
> }
>
>
> void main() {
>     S[2] a;
>     a[0].x = 42;
>
>     a = a.init;
>
>     assert(a[0].x == 0); // as expected the value has been reset
>     assert(dtorCount == 0); // Passes?!?
> }
> ---
>
> I would have expected this to either call opAssign or to destruct the
> instance, blit the init value, and call any postblits. However, as you can
> see neither the dtor nor opAssign are executed. If I add a postblit to S,
> then suddenly the dtor is invoked too.
>
> Am I missing something here, or is this a major bug in struct lifetime
> handling?
>
> I understand why this happens from the DMD source, but it almost seems
> like it was deliberately written this way; thus the question.
>
>  — David
>
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