On Wednesday, 17 February 2021 at 20:18:53 UTC, Paul Backus wrote:
On Wednesday, 17 February 2021 at 19:42:00 UTC, tsbockman wrote:
A copy constructor and opAssign can be used to update pointers
that are relative to &this:
https://dlang.org/spec/struct.html#struct-copy-constructor
Unfortunately this is not enough, because the compiler is free
to implicitly move struct instances in memory any time it wants
to. See the bug report below for more details:
https://issues.dlang.org/show_bug.cgi?id=17448
Until D gets move constructors, structs with interior pointers
should be avoided.
That bug is about postblits, this(this), not copy constructors:
this(ref typeof(this)). Copy constructors were added to the
language specifically to fix those sort of problems. From the
spec:
https://dlang.org/spec/struct.html#struct-postblit
WARNING: The postblit is considered legacy and is not
recommended for new code. Code should use copy constructors
defined in the previous section. For backward compatibility
reasons, a struct that explicitly defines both a copy
constructor and a postblit will only use the postblit for
implicit copying. However, if the postblit is disabled, the
copy constructor will be used. If a struct defines a copy
constructor (user-defined or generated) and has fields that
define postblits, a deprecation will be issued, informing that
the postblit will have priority over the copy constructor.
However, since issue #17448 is still open I have posted a
question to the issue report asking for clarification:
https://issues.dlang.org/show_bug.cgi?id=17448#c39
