Arrays passed by almost reference?

[Travis Boucher]

Leandro Lucarella wrote:
> Andrei Alexandrescu, el  5 de noviembre a las 16:10 me escribiste:
>> Ali Cehreli wrote:
>>> Thanks for all the responses.
>>>
>>> And yes, I know that 'ref' is what works for me here. I am trying to figure out whether I should develop a guideline like "always pass arrays with 'ref', or you may face surprises."
>>>
>>> I understand it very well now and was able to figure out a way to cause some bugs. :)
>>>
>>> What can be said about the output of the following program? Will main.a[0] be printed as 1 or 111?
>>>
>>> import std.cstream;
>>>
>>> void modify(int[] a)
>>> {
>>>    a[0] = 1;
>>>
>>>    // ... more operations ...
>>>
>>>    a[0] = 111;
>>> }
>>>
>>> void main()
>>> {
>>>    int[] a;
>>>    a ~= 0;
>>>    modify(a);
>>>
>>>    dout.writefln(a[0]);
>>> }
>>>
>>> It depends on the operations in between the two assignments to a[0] in 'modify':
>>>
>>> - if we leave the comment in place, main.a[0] is 111
>>>
>>> - if we replace the comment with this code
>>>
>>>    foreach (i; 0 .. 10) {
>>>        a ~= 2;
>>>    }
>>>
>>> then main.a[0] is 1. In a sense, modify.a caused only "some" side effects in main.a. If we shorten the foreach, then main.a[0] is again 111. To me, this is at an unmanagable level. Unless we always pass with 'ref'.
>>>
>>> I don't think that this is easy to explain to a learner; and I think that is a good indicator that there is a problem with these semantics.
>> The ball is in your court to define better semantics.
> 
> Just make arrays a reference value, like classes!
> 

You mean dynamic arrays, but what about static arrays?  Sometimes it 
makes more sense to send a static array as a value rather then a 
reference (think in the case of small vectors).

Then we'd have 2 semantics for arrays, one for static arrays and one for 
dynamic arrays.

I am not fully against pass-by-ref arrays, I just think in passing by 
reference all of the time could have some performance implications.