DIP 1021--Argument Ownership and Function Calls--Community Review Round 1

[David Bennett]

On Friday, 19 July 2019 at 01:32:34 UTC, Walter Bright wrote:
>
> One example is all that's necessary. Adding a bunch of 
> irrelevant code to it adds nothing.
>
> What part of the proposal are you not understanding?
>

For me it's unclear if the examples as given would become compile 
time errors because it states "The checks would only be enforced 
for @safe code." and the examples are not @safe.

Would the examples give errors in @system code or are they just 
there to illustrate buggy code and the idea being these could be 
made @safe with future work? (or both?)

Also, does it also check simple non-heap references, for example 
would this become compile time error?

---
@safe void f(scope ref int a, scope ref int b)
{
      a=1;
      assert(b==1);
}
@safe void main()
{
     int i = 0;
     f(i, i);
     assert(i==1);
}
---

Horrible code, but it compiles and runs with -dip1000 -dip25 
currently. https://run.dlang.io/is/XdQBzJ

If it's going to be an error, a simple example like this in the 
Breaking Changes and Deprecations section could help clear up 
whats changing from a practical sense.