On Monday, 2 April 2018 at 14:07:21 UTC, Steven Schveighoffer
wrote:
On 4/1/18 10:34 AM, ag0aep6g wrote:
On Sunday, 1 April 2018 at 13:37:43 UTC, Jonathan M Davis
wrote:
One issue is that postblit constructors fundamentally don't
work with const. The problem is that a postblit constructor
works by copying the object and _then_ mutating it, and you
can't mutate a const object.
I'm not so sure if that's fundamental. Can't we just say that
the copy is head-mutable at the time when the postblit
function is called, and it only becomes fully const after that?
The destination can't be const/immutable already, or you
wouldn't be able to write there anyway.
Yes, precisely what I had been arguing here:
https://issues.dlang.org/show_bug.cgi?id=18417#c5, however
const/immutable postblit was recently deprecated by:
https://github.com/dlang/dmd/pull/8032
So I don't think D is going to allow const postblit any more.
Maybe not even postblit any more.
-Steve
Andrei did post an example where treating the designation as
mutable, stuffing references to mutable data into is and then
treating it as immutable leaves you with an immutable reference
to immutable data.
However i think that loophole is fixed if you only allow
assignment to const/immutable from a pure postblit.
