Why is `scope` planned for deprecation?

[via Digitalmars-d]

On Wednesday, 12 November 2014 at 15:57:18 UTC, Nick Treleaven 
wrote:
> On 11/11/2014 18:01, bearophile wrote:
>> I agree it's a very important topic (more important/urgent 
>> than the GC,
>> also because it reduces the need of the GC). But I think 
>> Walter thinks
>> this kind of change introduces too much complexity in D 
>> (despite it may
>> eventually become inevitable for D once Rust becomes more 
>> popular and
>> programmers get used to that kind of static enforcement).
>
> I think Rust's lifetimes would be a huge change if ported to D. 
> In Rust user types often need annotations as well as function 
> parameters. People tend to want Rust's guarantees without the 
> limitations. I think D does need some kind of scope attribute 
> verification, but we need to throw out some of the guarantees 
> Rust makes to get an appropriate fit for existing D code.

Have you seen my proposal?

http://wiki.dlang.org/User:Schuetzm/scope

It takes a slightly different approach from Rust. Instead of 
specifying lifetimes, it uses owners, and it's also otherwise 
more simple than Rust's system. E.g. there is no full blown 
borrow checker (and no need for it).

>
> 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.