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

[Olivier FAURE]

On Wednesday, 31 July 2019 at 09:25:26 UTC, Walter Bright wrote:
> On 7/19/2019 9:39 AM, Timon Gehr wrote:
>> @safe:
>> class C{
>>      Array a;
>>      this(Array a){ this.a=move(a); }
>> }
>> 
>> void maybe_bad(C c, ref int i){
>>      c.a = Array();
>>      i++;
>> }
>> 
>> void main(){
>>      auto c=new C(Array());
>>      c.a.append(5);
>>      auto d=c;
>>      maybe_bad(c,d.a.get());
>> }
>
> Copying c to d will increase the ref count and so it will be 
> safe.

You misread the above example.

c is an instance of a class holding an Array, not an instance of 
an Array. So copying c to d doesn't involve calling Array's copy 
constructor.