Deprecating this(this)

[Timon Gehr]

On 02.04.2018 10:04, Shachar Shemesh wrote:
> On 02/04/18 10:45, Jonathan M Davis wrote:
>> Honestly, I think at this point pure is easier to understand if you 
>> think of
>> it as @noglobal and don't think about functional purity at all.
> 
> That's fine. My point was that the only optimizations possible are 
> possible on strictly pure functions (the immutable cast one included). 
> Weakly pure functions add nothing.
> ...

That point is wrong. It would be wrong even if your next point was true.

> But merely having them around means that when I annotate a function with 
> "pure", I do not promise any guarantees that the compiler can actually 
> use to perform optimizations.
> 
> Shachar

Yes, actually you do.

For example, if you have:

void foo(int[] x)pure;

void main(){
     auto x = [1];
     auto y = x.dup;
     foo(x);
     foo(y);
}

This can be transformed into:

void main(){
     auto x = [1];
     foo(x);
     auto y = x.dup;
}

Pure functions have deterministic side-effects.