copy constructors need documentation

[Manu]

On Tue, Aug 6, 2019 at 12:55 AM RazvanN via Digitalmars-d
<digitalmars-d at puremagic.com> wrote:
>
> On Tuesday, 6 August 2019 at 01:30:30 UTC, Manu wrote:
> > On Mon, Aug 5, 2019 at 2:10 AM RazvanN via Digitalmars-d
> > <digitalmars-d at puremagic.com> wrote:
> >>
> >> On Monday, 5 August 2019 at 09:01:39 UTC, Manu wrote:
> >> > On Mon, Aug 5, 2019 at 12:55 AM RazvanN via Digitalmars-d
> >> > <digitalmars-d at puremagic.com> wrote:
> >> >> [...]
> >> >
> >> > I'm so sorry, I completely missed that section of doco. It's
> >> > actually
> >> > quite comprehensive.
> >> > I don't know why I didn't find it initially when I went
> >> > looking.
> >> > Somehow the organisation didn't get me there.
> >>
> >> No worries!
> >>
> >> > It's a very tough read though, I had to jump around a lot;
> >> > like, I was
> >> > trying to work out why a qualified constructor works, and
> >> > that's
> >> > detailed in another section (which I still don't understand;
> >> > how can I
> >> > assign to an immutable `this`), but yeah, sorry for the false
> >> > alarm!
> >>
> >> Long story short: that's basically initialization of an
> >> immutable `struct`, therefore it is allowed. What I find weird
> >> is that you can define opAssign on `immutable` objects (wtf?!).
> >
> > So it's mutable for the time during initialisation?
> > `typeof(this) == T`?? not `immutable(T)`?
> >
> No. typeof(this) is going to be immutable(T) and `this` cannot be
> modified
> as in `this = something`, but the first assignment of each of
> this's field
> is considered initialization and allowed:
>
> struct T
> {
>      int a;
>      this(int a) immutable
>      {
>          pragma(msg, typeof(this));    // immutable(T)
>          this.a = a;                   // ok, even though this.a
> is immutable
>      }
> }
>
> Since this makes sense for constructors, it also makes sense for
> copy constructors as you may initialize an immutable object from
> a mutable one.

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