shared - i need it to be useful

[Manu]

On Sun., 21 Oct. 2018, 2:05 am Walter Bright via Digitalmars-d, <
digitalmars-d at puremagic.com> wrote:

> On 10/20/2018 11:30 AM, Manu wrote:
> > You can write an invalid program in any imaginable number of ways;
> > that's just not an interesting discussion.
>
> What we're discussing is not an invalid program, but what guarantees the
> type
> system can provide.
>
> D's current type system guarantees that a T* and a shared(T)* do not point
> to
> the same memory location in @safe code.
>

My proposal guarantees that too, but in a more interesting way, because it
opens the door to a whole working model. And it's totally @safe.

To get them to point to the same memory location, you've got to dip into
> @system
> code, where *you* become responsible for maintaining the guarantees.
>

My model preserves that property. Why do you think I'm running that static
guarantee?

It's all irrelevant if you don't express any mechanism to *do* anything.
Shared today does not have any use. It simply expresses that data *is*
shared, and says nothing about what you can do with it.
If you don't express a safe mechanism for interacting with shared data,
then simply expressing the distinction of shared data really is completely
uninteresting.
It's just a marker that's mixed up in a bunch of unsafe code. I'm no more
satisfied than I am with C++.

Shared needs to do something; I propose that it strictly models operations
that are threadsafe and semantic restrictions required to support that, and
then you have a *usage* scheme, which is safe, and API conveys proper
interaction.. not just an uninteresting marker.

I'm genuinely amazed that you're not intrigued by a @safe shared
proposition. Nobly likes @safe more than you.

I could run our entire SMP stack 100% @safe.

I am going to fork D with this feature one way or another. It's the most
meaningful and compelling opportunity I've seen in ever. If there's ever
been a single thing that could truly move a bunch of C++ programmers, this
is it. C++ can do a crappy job of modelling most stuff in D, but it simply
can't go anywhere near this, and I've been working on competing C++ models
for months.
SMP is the future, we're going all-in this generation. Almost every
function in our codebase runs in an SMP environment... And I was staggered
that I was able to work this definition through to such a simple and
elegant set of rules.
I can't get my head around why people aren't more excited about this...
fully @safe SMP is huge!

>
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