DIP60: @nogc attribute

[Steven Schveighoffer via Digitalmars-d]

On Mon, 21 Apr 2014 19:02:53 -0400, Walter Bright  
<newshound2 at digitalmars.com> wrote:

> On 4/21/2014 1:29 PM, Steven Schveighoffer wrote:
>> I think you are misunderstanding something. This is not for a pervasive
>> ARC-only, statically guaranteed system. The best example he gives (and  
>> I agree
>> with him) is iOS. Just look at the success of iOS, where the entire OS  
>> API is
>> based on ARC (actually RC, with an option for both ARC and manual, but  
>> the
>> latter is going away). If ARC was "so bad", the iOS experience would  
>> show it.
>> You may have doubts, but I can assure you I can build very robust and  
>> performant
>> code with ARC in iOS.
>
> The thing is, with iOS ARC, it cannot be statically guaranteed to be  
> memory safe.

So?

> This makes it simply not acceptable for D in the general case.

Because it can't live beside all the other unsafe code in D? I don't get  
it...

> It "works" with iOS because iOS allows all kinds of (unsafe) ways to  
> escape it, and it must offer those ways because it is not performant.

I think we're officially going in circles here.

> Kinda sorta memory safe, mostly memory safe, etc., is not a static  
> guarantee.
>
> There is JUST NO WAY that:
>
>      struct RefCount {
>          T* data;
>          int* count;
>      }
>
> is going to be near as performant as:
>
>      T*

Again with the straw man!

> 1. A dereference requires two indirections. Cache performance, poof!
>
> 2. A copy requires two indirections to inc, two indirections to dec, and  
> an exception unwind handler for dec.
>
> 3. Those two word structs add to memory consumption.

Consider the straw man destroyed :)

> As you pointed out, performant code is going to have to cache the data*  
> value. That cannot be guaranteed memory safe.
>
>
>>> I can't reconcile agreeing that ARC isn't good enough to be pervasive  
>>> with
>>> compiler technology eliminates unnecessary ARC overhead.
>> It's pretty pervasive on iOS. ARC has been around since iOS 4.3 (circa  
>> 2011).
>
> Pervasive means "for all pointers". This is not true of iOS. It's fine  
> for iOS to do a half job of it, because the language makes no  
> pretensions about memory safety. It is not fine for D to replace a  
> guaranteed memory safe system with an unsafe,  
> hope-your-programmers-get-it-right, solution.
>

Totally agree, which is why nobody is saying that.

-Steve