On 12/11/2014 17:16, "Marc Schütz" <schue...@gmx.net>" wrote:
On Wednesday, 12 November 2014 at 15:57:18 UTC, Nick Treleaven wrote:
For example, taking a mutable borrowed pointer for a variable means
you can't even *read* the original variable whilst the pointer lives.
I think no one would try to make D do that, but Rust's reason for
adding it is actually memory safety (I don't quite understand it, but
it involves iterator invalidation apparently). It's possible their
feature can be refined, but basically 'mut' in Rust really means
'unique'.
In my proposal, there's "const borrowing". It still allows access to the
owner, but not mutation. This is necessary for safe implementation of
move semantics, and to guard against iterator invalidation. It also has
other uses, like the problems with "transient range", e.g.
stdin.byLine(), which overwrite their buffer in popFront(). On the other
hand, it's opt-in; by default, owners are mutable while borrowed
references exist.
Looks good. Personally I've been meaning to study your (whole) proposal,
I think its a valuable analysis of what problems we could/should solve.
Just from a quick look, I wonder if 'const borrowing' could solve the
scoped!C premature destruction problem:
C c = std.typecons.scoped!C();
// memory for c has already been freed (need auto c = ...)
If the destruction of Scoped is disallowed whilst an (implicit alias
this) borrow for c is alive, the compiler can generate an error.
