Deprecating this(this)

[Jonathan M Davis]

On Sunday, April 01, 2018 10:31:46 Andrei Alexandrescu via Digitalmars-d 
wrote:
> On 4/1/18 9:37 AM, Jonathan M Davis wrote:
> > One issue is that postblit constructors fundamentally don't work with
> > const.
> Actually they do...

How so? In the postblit, you're dealing with a copy of an object where
everything is already initialized. Mutating the object would violate const.
It could be made to work for primitive types that the compiler understands
and knows that the member variable is truly independent - e.g. it could be
allowed to mutate an int, or it could be allowed to mutate a pointer while
treating what it points to as const, but as soon as you're dealing with
user-defined types, you're screwed - especially if you're dealing with
something like a struct with a user-defined opAssign. You're reading an
existing value and then mutating it, and it has to be at least tail-const,
because the original was const - and tail-const is pretty meaningless for
structs and can't really be represented in the type system for classes. So,
I don't see how postblit could be made to work with a const object of any
real complexity. It can be made to work in some corner cases but not in
general.

Kenji worked on a solution to the problem with const and postblit several
years ago (and I'm not sure how close he got to really solving it), but as I
recall, you and Walter shot it down because it was overly complicated. How
are you proposing that const work with postblit?

- Jonathan M Davis