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.
